Cytochrome p450ra1-2 and related proteins

ABSTRACT

The present invention provides a novel all-trans-RA inducible all-trans-RA metabolizing cytochrome P450, P450RAI-2, that is predominantly expressed in the brain, cerebellum in particular. Human P450RAI-2 show 42% amino acid identity to human P450RAI-1 and when transfected into COS-1 cells causes the rapid conversion of all-trans-RA into more polar metabolites including the inactive products 4-oxo-RA, 4-OH-RA and 18-OH-RA. P450RAI-2, as with P450RAI-1, is also inducible in certain cultured cell lines exposed to all-trans-RA. Methods for and uses of the new polynucleotide, polypeptide, fragments thereof and inhibitors thereof, include the treatment of dermatological disorders and cancer.

PRIOR APPLICATIONS

This application claims priority from U.S. Provisional Patent Application No. 60/171,110 filed Dec. 16, 1999 and U.S. Provisional Patent Application No. 60/178,314, filed Jan. 27, 2000 both of which are incorporated herein by reference.

FIELD OF THE INVENTION

The present invention relates to a novel gene encoding a polypeptide that is a member of the cytochrome P450 family. More particularly the present invention relates to a polynucleotide encoding the novel polypeptide, to an antisense polynucleotide thereof and to fragments thereof. The invention further relates to the novel cytochrome P450 as well as to vectors, host cells and antibodies to the polypeptide and the recombinant methods for producing the same. Uses and methods relating to any of the foregoing are also included within the scope of the invention.

BACKGROUND OF THE INVENTION

Cytochrome P450s

The cytochromes P450 comprise a large gene superfamily that encodes over 500 distinct heme-thiolate proteins that catalyze the oxidation of drugs and numerous other compounds in the body [Nelson et al., (1996); Guengerich (1991)]. Since there are at least 500 different cytochrome P450 enzymes, it is of considerable interest in the pharmaceutical and other fields to identify which of these enzymes are most important in the metabolism of individual compounds. There are now numerous examples of adverse drug-drug interactions and side effects that can now be understood in terms of the cytochrome P450 enzymes.

P450 proteins are ubiquitous in living organisms, and have been identified in bacteria, yeast, plants and animals [Nelson et al (1996); and Nelson, (1999a)]. The P450 enzymes catalyze the metabolism of a wide variety of drugs, xenobiotics carcinogens, mutagens, and pesticides, and are responsible for the bioactivation of numerous endogenous compounds including steroids, prostaglandins, bile acids and fatty acids body [Nelson et al., (1996); Guengerich (1991); Nebert et al., (1989)].

Cytochrome P450 metabolism of xenobiotics can result in detoxification of toxic compounds by their conjugation into excretable forms or can result in activation of compounds into metabolites that are toxic, mutagenic, or carcinogenic. Many steroids are deactivated by cytochrome P450-catalyzed oxidation.

Vitamin A and Retinoic Acid

Vitamin A metabolism gives rise to several active forms of retinoic acid (RA) which are involved in regulating gene expression during development, regeneration, and in the growth and differentiation of epithelial tissues. [Maden, 1992; Chambon, 1995; Mangelsdorf, 1995; Gudas, 1994; Lotan, 1995; Morriss-Kay, 1996] RA has been linked to apoptosis, or programmed cell death in a number of cell types; and to have anticarcinogenic and antitumoral properties [Lotan, 1996].

Early studies of retinol deficiency indicated a correlation between vitamin A depletion and a higher incidence of cancer and increased susceptibility to chemical carcinogenesis [Chytil, 1984]. Several animal models have been used to demonstrate the effectiveness of retinoids in suppressing carcinogenesis in a variety of tissues including skin, mammary epithelia, oral cavity, aerodigestive tract, liver, bladder and prostate [Moon, 1994]. These studies have led to the preventative use of retinoids to treat premalignant lesions including actinic keratosis and oral leukoplakia, as well as in the prevention of secondary tumors of the head and neck and the recurrence of non-small cell lung carcinomas, and basal cell carcinomas [Hong, 1994; Lippman, 1995]. RA itself has been found to be useful therapeutically, notably in the treatment of cancers, including acute promyelocytic leukemia (APL), tumors of the head and neck, and skin cancer, as well as in the treatment of skin disorders such as the premalignancy associated actinic keratoses, acne, psoriasis and ichthyosis. There is evidence that the effectiveness of RA as an anti-tumor agent is at least partially due to induction of cellular differentiation and/or inhibition of proliferation [Lotan, 1996]. Studies over the past several years indicate that a high proportion of patients with acute promyelocytic leukemia (APL) achieve complete remission after a short period of treatment with all-trans RA. Unfortunately, this high rate of remission is in most cases brief. Following relapse, patients are clinically resistant to further treatment with RA [Warrell, 1994; Warrell, et al., 1994; Chomienne, 1996; Muindi, 1992]. The nature of this resistance is unknown. Interestingly, leukemic cells taken from patients exhibiting clinical resistance to RA have been shown to be sensitive to the differentiating action of RA when grown in vitro [Muindi, 1992; Muindi, 1994]. This suggests that pharmacokinetic mechanisms may account for the acquired resistance to RA. This possibility is supported by studies showing that peak plasma concentrations of RA were much higher in patients after initial administration than in patients treated following relapse. This decrease in peak plasma RA concentration was accompanied by a 10-fold increase in urinary 4-oxo-retinoic acid concentration. In addition, ketoconazole, a broad spectrum inhibitor of cytochrome P450 function was shown to modulate RA pharmacokinetics in vivo [Muindi, 1992; Muindi, 1994]. It is therefore likely that RA increases the rate of its own metabolism which in turn results in the inability to sustain effective therapeutic doses of RA. Therapeutic administration of RA can result in a variety of undesirable side effects and it is therefore important to establish and maintain the minimal requisite doses of RA in treatment. For example, RA treatments during pregnancy can lead to severe teratogenic effects on the fetus. Adverse reactions to RA treatment also include headache, nausea, chelitis, facial dermatitis, conjunctivitis, and dryness of nasal mucosa. Prolonged exposure to RA can cause major elevations in serum triglycerides and can lead to severe abnormalities of liver function, including hepatomegaly, cirrhosis and portal hypertension.

RA metabolism may also account for the lack of response of certain tumors to RA treatment. For example, recent studies have shown that cytochrome P450 inhibitors that block RA metabolism, resulting in increased tissue levels of RA, may be useful therapeutic agents in the treatment of prostate cancer [Wouters, 1992; De Coster, 1996]. Thus RA metabolizing cytochrome P450s may be useful targets for the treatment of a number of different types of cancer.

The classical view of vitamin A metabolism holds that all trans-RA, the most active metabolite is derived from conversion of retinol to retinaldehyde to RA through two oxidation steps and that RA is further metabolized to the polar derivatives 4-OH RA and 4-oxo RA [Blaner, 1994; Napoli, 1995; Formelli, 1996; Napoli, 1996]. It is unknown whether the 4-oxo- and 4-OH-metabolites are simply intermediates in the RA catabolic pathway or whether they can also have specific activities which differ from those of all-trans RA and 9-cis RA. Pijnappel et al. [Pijnappel, 1993] have shown that, in Xenopus, 4-oxo-RA can efficiently modulate positional specification in early embryos and exhibits a more potent ability to regulate Hoxb-9 and Hoxb-4 gene expression than all-trans RA. 4-oxo-RA has been found to bind to retinoic acid receptor-β (RAR-β) with affinity comparable to all-trans RA [Pijnappel, 1993] but poorly to RAR-γ [Reddy, 1992], suggesting that this metabolite exhibits some receptor selectivity. 4-oxo-RA also binds to cellular retinoic acid binding protein (CRABP) but with an affinity slightly lower than that of all-trans RA [Fiorella, 1993]. Takatsuka et al. [Takatsuka, 1996] have shown that growth inhibitory effects of RA correlate with RA metabolic activity but it is unknown whether there is a causal relationship between production of RA metabolites and growth inhibition. The asymmetric distribution of these metabolites in developing embryos suggests that they may be preferentially sequestered or generated by tissue specific isomerases [Creech Kraft, 1994]. The normal balance of these metabolites is dependent upon rate of formation from metabolic precursors, retinol and retinaldehyde [Leo, 1989], and rate of catabolism. Little is presently known about the enzymes involved in this metabolic scheme, in particular the catabolism of RA.

The catabolism of RA is thought to be initiated by hydroxylation either at the C4-, or C18-position of the B-ionone ring of RA [Napoli, 1996]. The C4-hydroxylation step is mediated by cytochrome P450 activity, as judged by the ability of broad spectrum P450 inhibitors such as ketoconazole and liarazole to block 4-hydroxylation [Williams, 1987, Van Wauwe, 1988; Van Wauwe, 1990, Van Wauwe, 1992, Wouters, 1992]. In certain tissues, including testis, skin and lung and in numerous cell lines, such as NIH3T3 fibroblasts, HL 60 myelomonocytic leukemic cells, F9 and P19 murine embryonal carcinoma cell lines and MCF7, RA metabolism can be induced by RA pretreatment [Frolik, 1979, Roberts, 1979a and b; Duell, 1992; Wouters, 1992]. Studies involving targeted disruption of RAR genes in F9 cells suggest that RAR-α and RAR-γ isoforms may play a role in regulating the enzymes responsible for this increased metabolism [Boylan, 1995].

The glucuronidation of RA is a significant metabolic step in the inactivation of RA [Blaner, 1994; Formelli, 1996]. The elimination of RA may require oxidation to 4-oxo, followed by conjugation to form the 4-oxo all-trans RA glucuronide. This is supported by studies in both primates and humans showing that the 4-oxo RA glucuronide is the only retinoid conjugate found in urine [Muindi, 1992; Muindi, 1994]. The fact that following RA therapy, 4-oxo RA is not present or barely detectable in serum, suggests that oxidation may be the rate limiting step in this process.

It has recently been shown that 4-oxoretinol (4-oxo-ROL) can have greater biological activity than retinol. The 4-oxo-ROL is inducible by RA in F9 and P19 mouse teratocarcinoma cells [Blumberg et al., 1995; Achkar et al., 1996].

It is known that zebrafish fins regenerate through an RA sensitive process which utilizes many gene regulatory pathways involved in early vertebrate development [White, 1994; Akimenko, 1995a & b].

Cytochome P450s and Retinoic Acid Metabolism

In 1979, Roberts et al., [Roberts (1979a] first postulated that the catabolism of retinoic acid (RA) was mediated by a cytochrome P450 enzyme. Several P450s have since been shown to metabolize RA, including P450 proteins from human, zebrafish and mouse. For example, human P450RAI, which is induced by RA, metabolizes RA to more poplar derivatives including 4-hydroxy retinoic acid (4-OHRA) and 4-oxo retinoic acid (4-oxo RA) [White et al. (1996a)]. Since RA is useful as an antitumor agent, it is desirable to maintain high tissue levels of RA. Thus, cytochrome P450 inhibitors that block RA metabolism, resulting in increased tissue levels of RA, may be useful therapeutic agents in the treatment of cancers, such as prostate cancer [Wouters et al., (1992); and De Coster et al., (1996)].

International Patent Publication No. WO 97/49815, published Dec. 31, 1997, describes a family retinoid metabolizing proteins, CYP26A, including proteins from human, zebrafish and mouse and their coding sequences. This earlier publication is incorporated herein in its entirety. cDNAs encoding a cytochrome P450-dependent enzyme (P450RAI) which is induced by RA have been cloned and characterized from zebrafish and the protein metabolizes RA to more polar derivatives including 4-hydroxy retinoic acid (4-OH RA) and 4-oxo retinoic acid (4-oxo RA) [White et al., 1996a]. The identification of P450RAI gene is an important step in the understanding of RA signaling but its presence has been known since Roberts et al. (1979a) first postulated that the catabolism of RA was mediated by a P450 enzyme [Frolik et al., 1979; Roberts et al., 1979a]. More recently, the isolation of cDNAs which encode the full-length human and mouse P450RAI orthologs whose expression, like that of the fish cytochrome, is highly inducible by RA has been achieved [Fujii et al., 1997; Ray et al., 1997]. Human and mouse genomic P450RAI-1 sequences are identified herein as SEQ ID NOS: 15 and 16. The mouse sequence encoding P450RAI-1 is identified herein as SEQ ID NO: 17. Homologs have also been isolated from human, mouse, chick and xenopus all exhibiting a high degree of sequence conservation [Abu-Abed et al., 1998; Hollermann et al., 1998; White et al., 1997]. There is extensive identity between the human and fish P450RAI genes which overall is 68% at the amino acid level (over 90% between mouse and human).

MCF7 cells have been shown to have RA inducible RA metabolism [Butler and Fontana, 1992]; Wouters et al., 19921. The expression of P450RAI in these cells is dependent on the continuous presence of RA [White et al., 1997]. This suggests that P450RAI regulation by RA forms an autoregulatory feedback loop that functions to limit local concentrations of RA, such that when normal physiological levels of RA are exceeded, induction of P450RAI acts to normalize RA levels. The inducible expression of P450RAI in mouse embryos also suggests that a similar autoregulatory mechanism may limit exposure to RA sensitive tissues during development [Iulianella et al., 1999].

Retinoic Acid, Cytochrome p450 and Embryonic Development

All-trans-RA is a critical regulator of gene expression during embryonic development and in the maintenance of adult epithelial tissues [Gudas, et al. (1994); Lotan, R. M. (1995); Lotan, R. (1996); Morriss-Kay, G. M. (1996)]. The effects of all-trans-RA are mediated by heterodimers of nuclear receptors for retinoic acid (RARs) and retinoid-X-receptors, which are regulated by by the 9-cis isomer of RA. Three different subtypes exist for each of these receptors (RARα, β and γ, RXR RAR α, β and γ) which individually are expressed in a tissue specific manner but collectively can be found in essentially all cell types, both during embryonic development and in the adult [Chambon, P. (1995).]. The activity of RA in these tissues is controlled, to a large extent, by enzymes involved in its synthesis from retinaldehyde (ALDH-1 and RALDH-2) and its catabolism to 4-OH, 4-oxo and 18-OH products (P450RAI) [White J. A., et al. (1997); lulianella, A. et al. (1999); McCaffery P. et al., (1999) Niederreither, K. et al. (1999) Swindell E., et al. (1999)].

The present inventor and others have shown that P450RAI-1 (CYP26A) from zebrafish, mouse, human, chick and xenopus which is responsible for the metabolism of active all-trans-RA to inactive polar metabolites including 4-OH-RA, 4-oxo-RA and 18-OH-RA [White J., et al. (1997); Swindell E., et al. (1999); White, J. & Petkovich, M. (1996); Abu-Abed, et al. (1998); Fujii, H. et al. (1997); Ray, W. et al. (1997); Hollermann, T et al. (1998)]. P450RAI-1 expression can be induced by all-trans-RA pre-treatment in multiple tissues, and cell types, and this expression is concomitant with increased all-trans-RA catabolism. In MCF7 cells, all all-trans-RA suggesting a feedback-loop mechanism is dependent on the continued presence of all-trans-RA suggesting a feedback-loop mechanism for the regulation of all-trans-RA levels [White J., et al. (1997)]. Inducible expression of P450RAI-1 has also been observed in vivo in zebrafish, chick, xenopus and mouse embryos suggesting that this autoregulatory feedback-loop plays an important role in balancing all-trans-RA levels in certain developing tissues.

Studies from several groups show that tissues such as neural folds in chick embryos [Swindell E., et al. (1999)], caudal neuroepithelia [Iulianella, A et al. (1999); Fujii, H. et al. (1997)] and developing retina [McCaffery P. et al. (1999)] from mouse express P450RAI-1 constitutively thus forming a barrier to all-trans-RA exposure. Comparison of the expression patterns of RALDH-2 and P450RAI-1 in these models suggest that these enzymes act together to form regions of RA synthesis and activity (where RALDH-2 is expressed). RALDH-2 expressing tissues have been shown to contain retinoid activity as measured by both retinoid responsive reporter gene activity and direct measurement of RA levels from tissue extracts; by similar analyses, P450RAI-1 expressing tissues do not [Iulianella, A et al. (1999); McCaffery P. et al. (1999)]. In addition, over expression of P450RAI-1 in xenopus embryos has been shown to abrogate the teratogenic effects of exogenously applied RA, consistent with a catabolic role for its enzyme [Hollermann, T et al. (1998)].

SUMMARY OF THE INVENTION

The present inventors have identified and characterized a novel cytochrome P450 that can metabolize retinoic acid, preferably all-trans retinoic acid, (hereinafter referred to as P450RAI-2) and the nucleic acid sequence encoding therefor.

In one embodiment the P450RAI-2 is a mammalian P450RAI-2, and preferably a murine, rat or human P450RAI-2. In an another embodiment the P450RAI-2 is a zebrafish P450RAI-2.

Although, the P450RAI-2 and encoding nucleic acid sequence of the invention can be isolated and characterized from a number of different tissues such as spleen, kidney, skeletal muscle, brain, liver, retina, heart or small intestine, it is preferably isolated and characterized from brain cells, such as from from the cerebellum, cerebal cortex, medulla, occipital pole, frontal lobe and temporal lobe, and most preferably from the cerebellum.

Accordingly, the present invention provides an isolated nucleic acid molecule comprising a sequence encoding a P450RAI-2, preferably a human P450RAI-2 or a murine P450RAI-2 or fragments thereof.

In a preferred embodiment, an isolated nucleic acid molecule is provided having: (a) a nucleic acid sequence as shown in SEQ ID NOS: 4, 5, 28, 27, 7, 18, 26, 21, 22, 23, 24, or 25 where T can also be U; (b) nucleic acid sequences complementary to (a); (c) nucleic acid sequences which are homologous to (a) and (b); (d) a nucleic acid molecule differing from any of the nucleic acid molecules of (a) to (c) in codon sequences due to the degeneracy of the genetic code; or (e) a fragment of (a) to (d) that is at least 15 bases, preferably 20 to 30 bases, and which will hybridize to (a) to (c) under stringent hybridization conditions.

The present invention also includes the P450RAI-2 polypeptide itself. Accordingly, the invention provides a polypeptide having an amino acid sequence of a P450RAI-2. Preferably, the invention provides a polypeptide having either the human (SEQ ID NO: 5) or a homologous mouse sequence or fragment thereof. The invention also comprises peptides comprising fragments of the amino acid sequence of SEQ ID NO: 5. Preferably the fragments comprise amino acid sequences of SEQ ID NOS: 11 or 12 or encoded by nucleic acid sequences SEQ ID NOS. 18, 26, or 21 to 25. In another embodiment the fragments preferably comprise at least 14 amino acid residues and are most preferably antigenic or immunogenic. In one embodiment the invention provides peptides encoded by a nucleic acid sequence of SEQ ID NO: 4 or fragments thereof and to an antisense nucleic acid molecule to all or part of the nucleic acid molecule encoding P450RAI-2.

In another embodiment, homologs, analogs, and modifed proteins of the invention as described herein are encompassed within the scope of this invention.

In one embodiment, the invention also provides a nucleic acid molecule of the invention operationally linked to an expression control sequence in a suitable expression vector. In another embodiment, the expression vector comprising the nucleic acid molecule of the invention is capable of being activated to express the peptide which is encoded by the nucleic acid molecule and is capable of being transformed or transfected into a suitable host cell. Such transformed or transfected cells are also encompassed with the scope of this invention.

The invention also provides a method of preparing a P450RAI-2 protein of the invention utilizing a nucleic acid molecule of the invention. In one embodiment, a method for preparing a P450RAI-2 protein of the invention is provided comprising: transforming a host cell with a recombinant expression vector comprising a nucleic acid sequence of the invention; (b) selecting transformed host cells from untransformed host cells; (c) culturing a selected transformed host cell under conditions which allow expression of the protein; and (d) isolating the protein.

The invention also encompasses an antibody specific for one or more epitopes of a protein of the invention, such as a peptide specific antibody or a polyclonal antibody, and more preferably a monoclonal antibody. The invention also encompasses methods for preparing the antibodies. Preferably the epitopes are selected from the group consisting of SEQ ID NOS: 5, 11, 12, or those encoded by nucelic acid sequences SEQ ID NOS; 4, 6, 8, 18, 21-25, 27 or 28 or immunogenic fragments thereof.

The invention also includes a method for detecting a disease or medical condition associated with P450RAI-2 expression or RA metabolism in an animal. “A disease or medical condition associated with P450RAI-2 expression” as used herein means any disease that can be affected or characterized by the level of P450RAI-2 expression. This includes, without limitation, diseases affected by, high, normal, reduced or non-existent expression of P450RAI-2 or expression of mutated P450RAI-2. A disease or medical condition associated with P450RAI-2 expression includes diseases associated with RA metabolism such as cell cycle regulation, particularly cell growth and apoptosis, for instance cancer, dysplasia, autoimmune disease, dermatological disorders and disabilities associated with high order brain functions, such as learning and memory. The method comprises assaying for the P450RAI-2 from a sample, such as a blood sample, a biopsy, or other cellular or tissue sample, from an animal susceptible of having such a disease. In one embodiment, the method comprises contacting the sample with an antibody of the invention that binds P450RAI-2, and measuring the amount of antibody bound to P450RAI-2 in the sample, or unreacted antibody. In another embodiment, the method involves detecting the presence of a nucleic acid molecule having a sequence encoding a P450RAI-2, comprising contacting the sample with a nucleotide probe which hybridizes with the nucleic acid molecule, preferably mRNA or cDNA to form a hybridization product under conditions which permit the formation of the hybridization product, and assaying for the hybridization product.

The invention further includes a kit for detecting a disease or condition associated with P450RAI-2 expression in a sample comprising an antibody of the invention, preferably a monoclonal antibody. Preferably directions for its use is also provided. The kit may also contain reagents that are required for binding of the antibody to a P450RAI-2 protein in the sample.

The invention also provides a kit for detecting the presence of a nucleic acid molecule having a sequence encoding a polypeptide related to or analogous to a polypeptide of the invention, comprising a nucleotide probe which hybridizes with the nucleic acid molecule, reagents required for hybridization of the nucleotide probe with the nucleic acid molecule, and directions for its use.

The invention further provides a method of treating or preventing a medical condition disease associated with P450RAI-2 or RA expression comprising administering an effective amount of an agent that activates, simulates or inhibits P450RAI-2 expression, as the situation requires, to an animal in need thereof. In a preferred embodiment, P450RAI-2, a therapeutically active fragment thereof, or an agent which activates or simulates P450RAI-2 expression is administered to the animal in need thereof to treat cancer, dysplasia, autoimmune disease or dermatological disorders or to improve high order brain functions or dermatological disorders. In another embodiment the disease is associated with over expression of P450RAI-2 or too little apoptosis, and the method of treatment comprises adminstration of an effective amount of an agent that inhibits P450RAI-2 expression such as an antibody to P450RAI-2, a mutation thereof, or an antisense nucleic acid molecule to all or part of the P450RAI-2 gene.

In another embodiment, the invention provides pharmaceutical compositions comprising the nucleic acid molecules of proteins, antibodies, vectors or cells of the invention and a pharmaceutically acceptable carrier.

In another embodiment, the invention further provides a method for identifying modulators of P450RAI-2 expression or P450RAI-2 activity.

In yet another embodiment, the invention further provides a method of rational drug design.

In one embodiment the invention provides methods or uses of the proteins and nucleic acid molecules of the invention, such as in relation to medical treatment.

Other objects, features and advantages of the present invention will become apparent from the following detailed description. It should be understood, however, that the detailed description and the specific examples, while indicating preferred embodiments of the invention, are given by way of illustration only. Various changes and modifications within the spirit and scope of the invention will become apparent to those skilled in the art from this detailed description.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic diagram showing the 6 exons of human cytochrome p450RAI-2 on human clone having GenBank Accession No. AC007002 (SEQ ID NO:3). The numbers above the schematic diagram indicate the amino acid regions of the exons and the numbers below the schematic refer to nucleotide positions on the human sequence.

FIG. 2 Human P450RAI-2 cDNA sequence (SEQ ID NO: 28) comprising the coding sequence and the 3′ untranslated sequence. The full-length cDNA clone was isolated from human retina cDNA. The deduced primary sequence using single-letter amino acid codes, identifies a 512 amino acid protein which is shown directly below the corresponding nucleotide sequence. Numbers on the right refer to the nucleotide positions.

FIG. 3 Sequence comparison between human P450RAI-2 and human P450RAI-1. Predicted amino acid sequences were aligned using Omiga software (Oxford Molecular, CA). Identical amino acids are highlighted by the black boxes with white letters. Conservatively substituted amino acids are indicated by the open boxes. Gaps, indicated by the dashes, have been introduced in several regions in order to optimize amino acid identity between the two proteins. Overall the two protein sequences show 42% identity at the amino acid level. Numbers on the right hand side refer to the corresponding amino acid positions.

FIG. 4 Expression of P450RAI-2 in human tissues. RNA samples from 76 normal human tissues were probed for expression of P450RAI-2 transcripts using a commercially available dot blot (A). Signals representing P450RAI-2 transcripts are observed in three samples, a2, b2 and h1 representing left and right cerebellum and pons respectively. Sample a1 is whole brain and a11 is fetal brain for comparison. Control hybridization with a human ubiquitin probe (B) shows differences in RNA loading. Northern blot analyses for expression of P450RAI-2 expression in human brain (D). 2 μg poly A+ mRNA each from eight different human brain tissues was used to analyze P450RAI-2 expression. Transcripts at approximately 5 Kb corresponding to P450RAI-2 are indicated, with the highest levels of expression seen in cerebellum.

FIG. 4C shows the location of the different human mRNAs on the blot used in FIG. 4A.

FIG. 5 shows northern blot analysis of human cell lines probed with an α-[³²P]-dATP labeled probe having the sequence identified as SEQ ID NO:4 SKMES; CALU-1 and MCF-7 (A). Cells were treated with DMSO, all-trans retinoic acid, 9-cis retinoic acid or 13-cis retinoic acid. Cells were exposed to 10⁻⁶ M final concentrations of each retinoid dissolved in DMSO. Transcripts corresponding to P450RAI-2 are indicated by the arrowhead. The blot was also probed with the human β-actin probe to control for RNA loading of the gel, shown in the middle panel (B). The 18S and 28S portions of the mRNA as seen on the ethidium bromide stained agarose gel are shown in the bottom panel (C).

FIG. 6 is similar to FIG. 5 except that the cells, HPK1A-RAS, were treated with either DMSO or all-trans retinoic acid.

FIG. 7 All-trans-RA induction of P450RAI-2 expression. Northern blot analysis (A) of cultured cells treated with all-trans-RA or vehicle (DMSO). P450RAI-2 hybridizing transcripts are identified. The positions of 28S and 18S ribosomal RNA are indicated along with the ethidium bromide stained gel showing the relative abundance of RNA in all samples. Multiple other cell lines were tested using semiquantitative RT-PCR and southern blotting (B). Transcripts for P450RAI-2 are regulated in a cell specific manner. P450RAI-2 is constitutively expressed in SK-MES-1 and SW900 and possibly WTE; inducible in MCF-7, HPK1a-ras and HeLa; and undetectable in SK-Luci-6, V79 or NB4. A timeline of induction of mRNAs, for P450RAI-2 in HPK1a-ras cells (C). Within 2 hours of addition of all-trans-RA maximal induction of transcripts for P450RAI-2 is observed. GAPDH controls are shown below for each RNA sample analyzed.

FIG. 8A shows the total aqueous soluble radioactivity measured using aliquots of the aqueous soluble extracts from media alone, as well as cells transfected with pcDNA3.1, pcDNA3.1-CYP26A (human) (i.e., P450RAI) or pcDNA-P450RAI-2. Aqueous soluble extracts were subjected to B-scintillation counting.

FIG. 8B shows a summary of the peak integration analysis performed after HPLC on the organic soluble radioactivity. Samples were the same as in FIG. 8A. Cells transfected with either pcDNA3.1-CYP26A (human) or pcDNA3.1-P450RAI-2 show a decrease in all-trans retinoic acid substrate with a concomitant increase in the production of 4-OH-retinoic acid, 4-oxo-retinoic acid and more polar peaks.

FIG. 9 shows the same analysis as FIG. 8B except that cells were treated with 1 μM non-radioactive all-trans-retinoic acid.

FIG. 10 shows a control HPLC trace from media alone in the absence of the COS-1 cells. An all-trans-retinoic acid substrate peak is observed at 20.808 minutes. Peaks at 1.409 and 1.874 are contaminants not characteristic of retinoids. The top panel shows photo diode array detection of the peaks. Retinoids have characteristic UV maxima in the range of about 320 to about 380 nM.

FIG. 11 is similar to FIG. 10 except that the sample is from COS-1 cells transfected with the pcDNA3.1 plasmid alone.

FIG. 12 is similar to FIG. 10 except that the sample is from COS-1 cells transfected with pcDNA3.1-P450RAI. Multiple more polar peaks characteristic of retinoids are generated in these cells. Peaks which co-elute with standards for 4-OH-retinoic acid and 4-oxo-retinoic acid were observed at 8.191 and 9.661 minutes respectively. Additional peaks which have not been characterized are also evident.

FIG. 13 is similar to FIG. 12 except that the sample is from COS-1 cells transfected with pcDNA3.1-P450RAI-2.

FIG. 14 shows HPLC analysis of all-trans-RA metabolism. COS-1 cells were transiently transfected with pcDNA3.1-P450RAI-2 (A), pcDNA3.1-P450RAI-1 (B) or pcDNA3.1 alone (C) and exposed to μM all-trans-RA for 3 hours. Incubation with RA was followed by total lipid extraction of the media and subsequent HPLC analysis using a reverse-phase system. Expression of either P450RAI-2 or P450RAI-1 in cells causes disappearance of all-trans-RA substrate (compare C to A or B) in addition to the generation of more polar metabolic products. Identities of the retinoids labeled as all-trans-RA, 4-OH-RA, 4-oxo-RA and 18-OH-RA (A and B) were verified by co-elution with known standards and comparison of the spectral properties of the peaks using photodiode array detection. Multiple polar peaks are observed in P450RAI-2 expressing cells exposed to all-trans-RA. Peaks labeled 1-4 (A) have spectral properties characteristic of retinoids, specifically a UV maxima of between 320 and 350 nm. The exact identity of these polar metabolites remains to be established.

FIG. 15 shows metabolism of all-trans-RA. COS-1 cells transiently transfected with pcDNA3.1-P450RAI-2, pcDNA3.1-P450RAI-1 or pcDNA3.1 alone and exposed to 100 nM [³H]all-trans-RA for 3 hours. Conversion of all-trans-RA to aqueous-soluble metabolites is observed in P450RAI-2 or P450RAI-1 expressing cells compared to pcDNA vector or media alone control samples (A). Using HPLC analysis with subsequent β-scintillation counting was used to evaluate the lipid-soluble retinoids generated from P450RAI-2 or P450RAI-1 expressing cells. Fractions from chromatography were grouped into three regions, all-trans-RA substrate, 4-OH region and polar region allowed quantification of the retinoid metabolites. Levels of all-trans-RA remaining after incubation were substantially decreased in P450RAI-2 or P450RAI-1 transfected cells compared to controls (B). Additionally, there is an increase in radioactivity representing both the 4-OH and polar regions (B).

FIG. 16 A-D is competitive inhibition of P450RAI-mediated all-trans-RA metabolism. COS 1 cells transiently transfected with pcDNA3.1-P450RAI-2, pcDNA3.1-P450RAI-1 or pcDNA3.1 alone were used to assess the ability of several retinoids to competitively inhibit all-trans-RA metabolism. Cells were exposed to 2 nM [³H]all-trans-RA with increasing concentrations of unlabelled competitor and assayed for generation of aqueous soluble radioactivity. Panels on the right show cells expressing P450RAI-2 with panels on the left showing cells expressing P450RAI-1. 9-cis-RA and 13-cis-RA (top panels) are less effective than all-trans-RA as competitors for either P450RAI-2 or P450RAI-1. Retinol and retinal were similarly tested (bottom panels) and found to be less effective competitors. For comparison, the nonspecific cytochrome P450 inhibitor ketoconazole is shown in each panel.

FIG. 17 shows Northern blot (A) and RT-PCR (B) results for total RNA samples from the various cell samples designated.

FIG. 18 shows expression of P450RAI-2 in 8.0 and 8.5 dpc mouse embryos. (A) 8.0 dpc lateral view. No apparent staining. (B) 8.0 dpc, dorsal view. Staining at anterior end of neutral folds. (C) 8.5 dpc, lateral view. Expression is evident, possibly in presumptive rhombmeres 2, 5, and 6. (D) 8.5 dpc, dorsal view, rhombomere expression of RAI2 is clearly evident. TL: Tail; YS Yolk Sac; NF: Folds; pr: Presumptive Rhombomeres.

FIG. 19 shows expression of P450RAI2 in 9.0 and 10.5 dpc mouse embyros. (A) 9.0 dpc, lateral view. Specific staining is visible in the eye, and rhombomeres 5 and 6. Diffuse staining is visible where the hind bud is beginning to form. (B) 9.0 dpc, dorsal view. Rhombomeres 5 and 6 show RAI2 expression. (C) 10.5 dpc, lateral view. The otic vesicle and eye are stained. (D) 10.5 dpc, dorsal view. Specific staining is observed in both otic vesicles as well as as the hind linb bud. HL: hind limb bud; OV: Otic Vesicle.

FIG. 20 shows expression of P450RAI2 staining in 11.5 dpc mouse embryo(A) 11.5 dpc, laterial view, staining is visible in both the fore and hindlimb bud. (B) 11.5 dpc, ventral view. Expression of RAI2 in both limb buds (C) Close up of forelimb bud, showing a lack of expression in the apical ectodermal ridge FL: Forelimb bud; HL: Hindlimb bud; AR: Apical Ectodermal Ridge.

FIG. 21 shows P450RAI2 staining in embryos treated with Retinoic Acid (A) 8.5 dpc, lateral view, staining is observed in rhombomere 5 and the tail mesoderm as indicated by the arrow. (B) 8.5 dpc, dorsal view clearly showing P450RAI2 expression in rhombomere 5. (C) 9.5 dpc, lateral view, expresion of P450RAI2 is observed in rhombomeres 5 and 6, the developing hindlinb, somites and posterior mesoderm. (D) 9.5 dpc, dorsal view, expression is evidenct in rhombomeres 3,5 and 6 and in trunk ectoderm as indicated by the arrow. r: rhombomere; HL; Limb bud.

FIG. 22 shows P450RAI2 expression in 11.5 dpc embryos treated with retinoic acid. (A) 11.5 dpc, lateral view, P450RAI2 expression is observed in both the developing hind and fore limb. (B) 11.5 dpc, ventral view, as in embryos untreated with retinoic acid, P450RAI2 expression is not observed in the aptical ectodermal ridge.

DETAILED DESCRIPTION OF THE INVENTION

Retinoids, particularly all-trans retinoic acid (all-trans-RA), are potent regulators of cell differentiation, cell proliferation and apoptosis. As noted above, the role of all-trans-RA during development and in the maintenance of adult tissues has been well established. The control of all-trans-RA in cells and tissues is regulated by the balance between its biosynthesis and its catabolism to inactive metabolites. The cytochrome P450 enzyme P450RAI-1 is partially responsible for this inactivation of all-trans-RA.

The present inventors have now identified, cloned and characterized a second related enzyme, here termed P450RAI-2, which is also involved in the specific inactivation of all-trans-RA. A cDNA has been isolated from human retina and sequenced. A protein encoded by the cDNA has been expressed and shown to have the ability to metabolize all-trans-RA to more polar metabolites. The metabolites so formed include products that have been oxidized at the 4-position of the β-ionone ring, including the corresponding acid hydroxylated at the 4-position of the β-ionone ring. The mRNA has been found to be inducible in multiple cell types including but not limited to human lung and human skin upon the addition of all-trans retinoic acid.

The present inventors herein show that tansiently transfected P450RAI-2 can convert all-trans-RA to more polar metabolites including 4-oxo, 4-OH, and 18-OH-retinoic acid. Competition experiments with other retinoids suggest that all-trans-RA is the preferred substrate, but not necessarily the only retinoid substrate. The high level of expression of P450RAI-2 particularly in the cerebellum and pons of human adult brain, suggests a unique role for this enzyme in the protection of specific tissues from exposure to retinoids.

Homologs of the cloned sequence have also been identified. Partial nucleotide sequences have been determined for the mouse, rat and zebrafish P450RAI-2 coding sequence.

Definitions

The term “retinoids” as used herein means a group of compounds which includes retinoic acid, vitamin A (retinol) and a series of natural and synthetic derivatives that can exert profound effects on development and differentiation in a wide variety of systems. For purposes of this disclosure “retinoid” is also intended to encompass an equivalent thereof having the same functional characteristics which may be produced, for example, by computational chemistry.

The following standard abbreviations for the amino acid residues are used throughout the specification: A, Ala—alanine; C, Cys—cysteine; D, Asp—aspartic acid; E, Glu—glutamic acid; F, Phe—phenylalanine; G, Gly—glycine; H, His—histidine; I, Ile—isoleucine; K, Lys—lysine; L, Leu—leucine; M, Met—methionine; N, Asn—asparagine; P, Pro—proline; Q, Gln—glutamine; R, Arg—arginine; S, Ser—serine; T, Thr—threonine; V, Val—valine; W, Trp—tryptophan; Y, Tyr—tyrosine; and p.Y., P.Tyr—phosphotyrosine.

I. Nucleic Acid Molecules of the Invention

The present invention provides an isolated nucleic aid molecule comprising a sequence encoding a cytochrome P450RAI-2 polypeptide.

The term “isolated” refers to a nucleic acid substantially free of cellular material or culture medium when produced by recombinant DNA techniques, or chemical precursors, or other chemicals when chemically synthesized.

The term “nucleic acid molecule” is intended to include unmodified DNA or RNA or modified DNA or RNA. For example, the nucleic acid molecules or polynucleotides of the invention can be composed of single- and double stranded DNA, DNA that is a mixture of single- and double-stranded regions, single- and double stranded RNA, and RNA that is a mixture of single- and double-stranded regions, hybrid molecules comprising DNA and RNA that may be single-stranded or, more typically double stranded or a mixture of single- and double stranded regions. In addition, the P450RAI-2 nucleic acid molecules can be composed of triple-stranded regions comprising RNA or DNA or both RNA and DNA. The nucleic acid molecules of the invention may also contain one or more modified bases or DNA or RNA backbones modified for stability or for other reasons. “Modified” bases include, for example, tritiated bases and unusual bases such as inosine. A variety of modifications can be made to DNA and RNA; thus “nucleic acid molecule” embraces chemically, enzymatically, or metabolically modified forms. The term “polynucleotide” shall have a corresponding meaning.

One aspect of the present invention is thus an isolated nucleic acid molecule comprising a nucleotide sequence selected from the group consisting of:

(a) a nucleotide sequence as shown in SEQ ID NOS: 4 or 28, but preferably SEQ ID NO: 4, wherein T can also be U;

(b) nucleotide sequences complementary to (a);

(c) nucleotide sequences which are homologous to (a) or (b);

(d) a nucleotide sequence differing from any of the nucleotide sequences of (a) to (c) in codon sequences due to the degeneracy of the genetic code; or

(e) a fragment of (a) to (d) that is at least 15 bases, preferably 20 to 30 bases, and which would hybridize to (a) to (d) under stringent hybridization conditions. In another embodiment, the fragment is at least 35, 40, 45, 50, 55, or 60 or more nucelotides in length. In another embodiment the fragment is capable of oxidizing a retinoid. In yet another embodiment it preferably has at least about 55 percent homology with the protein encoded by a nucleotide sequence of (a) or (b).

In another embodiment, the nucleotide sequence in (a) above is a human P450RAI-2 sequence. In one embodiment, the nucleic acid sequence can be used as a probe or a primer, such as for PCR, like SEQ ID NOS: 9, 10, 29, 30, 33, 37 or 38. In yet another embodiment, the nucleotide sequence of (a) above is selected from the group consisting of: a mouse P450RAI-2 sequence, such as SEQ ID NO: 6, 18, 26, 21, 22, 23, 24 or 25; a rat P450RAI-2 sequence, SEQ ID NO: 27; or a zebrafish P450RAI-2 sequence, SEQ ID NO: 8.

In one embodiment, the nucleic acid molecule of the invention encodes a protein that is capable of oxidizing a retinoid, preferably retinoic acid, preferably at the 4-position of the β-ionone ring. In another embodiment the nucleic acid molecule of the invention encodes a protein having SEQ ID NO: 5. In another embodiment, the nucleotide sequence inhibits P450RAI-2 expression, such as certain complimentary sequences to SEQ ID NO 4.

In one embodiment of the invention, the nucleic acid molecule consists of any of the nucleotide sequences described herein.

In all of the sequences referred to above, T can also be U. As previously stated, the invention includes isolated DNA molecules having such sequences of nucleotides, and RNA molecules having such sequences. The invention thus includes isolated mRNA transcribed from DNA having such a sequence. The invention further encompasses nucleic acid molecules that differ from any of the nucleic acid molecules of the invention in codon sequences due to the degeneracy of the genetic code.

The invention also encompasses nucleic acid sequences or molecules that are analogs of the nucleic acid sequences and molecules described herein. The term “a nucleic acid sequence which is an analog” means a nucleic acid sequence which has been modified as compared to the sequences described herein, such as sequences of (a), (b), (c), (d), or (e), above wherein the modification does not alter the utility of the sequences described herein. The modified sequence or analog may have improved properties over the sequence shown in (a), (b), (c), (d) or (e). One example of a modification to prepare an analog is to replace one of the naturally occurring bases (i.e. adenine, guanine, cytosine or thymidine) of the sequence shown in SEQ ID NO: 4, 6, 8-10, 18, or 21-28 with a modified base such as such as xanthine, hypoxanthine, 2-aminoadenine, 6-methyl, 2-propyl and other alkyl adenines, 5-halo uracil, 5-halo cytosine, 6-aza uracil, 6-aza cytosine and 6-aza thymine, pseudo uracil, 4-thiouracil, 8-halo adenine, 8-aminoadenine, 8-thiol adenine, 8-thiolalkyl adenines, 8-hydroxyl adenine and other 8-substituted adenines, 8-halo guanines, 8 amino guanine, 8-thiol guanine, 8-thiolalkyl guanines, 8-hydroxyl guanine and other 8-substituted guanines, other aza and deaza uracils, thymidines, cytosines, adenines, or guanines, 5-trifluoromethyl uracil and 5-trifluoro cytosine.

Another example of a modification is to include modified phosphorous or oxygen heteroatoms in the phosphate backbone, short chain alkyl or cycloalkyl intersugar linkages or short chain heteroatomic or heterocyclic intersugar linkages in the nucleic acid molecule shown in SEQ ID NOS: 4, 6, 8-10, 18, or 21-28. For example, the nucleic acid sequences may contain phosphorothioates, phosphotriesters, methyl phosphonates, and phosphorodithioates.

A further example of an analog of a nucleic acid molecule of the invention is a peptide nucleic acid (PNA) wherein the deoxyribose (or ribose) phosphate backbone in the DNA (or RNA), is replaced with a polyamide backbone which is similar to that found in peptides (P. E. Nielsen, et al Science 1991, 254, 1497). PNA analogs have been shown to be resistant to degradation by enzymes and to have extended lives in vivo and in vitro. PNAs also bind stronger to a complimentary DNA sequence due to the lack of charge repulsion between the PNA strand and the DNA strand. Other nucleic acid analogs may contain nucleotides containing polymer backbones, cyclic backbones, or acyclic backbones. For example, the nucleotides may have morpholino backbone structures (U.S. Pat. No. 5,034,506). The analogs may also contain groups such as reporter groups, a group for improving the pharmacokinetic or pharmacodynamic properties of nucleic acid sequence.

It will be appreciated that the invention includes nucleic acid molecules encoding truncations of proteins of the invention, and analogs and homologs of proteins of the invention and truncations thereof, as described below. It will further be appreciated that variant forms of nucleic acid molecules of the invention which arise by alternative splicing of an mRNA corresponding to a cDNA of the invention are encompassed by the invention. The invention further includes biologically active fragments of the nucleic acid molecules of the invention. Such fragments would include, but is not necessarily limited to any nucleic acid molecules which are beneficial in the modulation, including but not limited to simulation, inhibition or stimulation of P450RAI-2 activity or P450RAI-2 expression, or in the identification or production of such agents.

A nucleic acid molecule of the invention can encode a protein (polypeptide) having a homology of at least about 50, at least about 55, or more preferably at least about 58 percent with a protein encoded by SEQ ID NO:4 or the full length anti-sense sequence thereto. The level of homology, according to various aspects of the invention is at least about 60 percent; at least about 63 percent; at least about 65 percent; at least about 68 percent; at least about 70 percent; at least about 73 percent; at least about 75 percent; at least about 78 percent; at least about 80 percent; at least about 83 percent; at least about 85 percent; at least about 88 percent; at least about 90 percent; at least about 93 percent; at least about 95 percent; or at least about 98 percent. Methods for aligning the sequences to be compared and determining the level of homology between the sequences are described in detail below.

In another aspect, the present invention includes a fragment of the nucleotide sequence encoding P450RAI-2 (SEQ ID NO:4). Such a fragment can find usefulness as a probe or depending on the fragment may even have biological activity itself. The complement of the probe can find utility in, for example, manufacture of the probe or inhibition of any activity of the fragment, as the case may be. In a particular use, the probe can be used to determine the presence of an RNA molecule in a sample which might, or might not, also include an RNA molecule encoding P450RAI-1. Such a probe would generally be 20 nucleotides long or be at least 20 nucleotides long. The probe could also be 25, 30, 35, 40, 45, 50, 55, 60 or more nucleotides in length and the probe can include the full length of the complement to the sequence to which it is intended to bind. The sequence of the probe would also be sufficiently distinguishable from any portion of the sequence encoding P450RAI-1 that it would not cross-hybridize to a significant extent to a nucleotide sequence that encodes P450RAI-1, or portion thereof, particularly to an RNA encoding P450RAI-1. Such a probe would thus be sufficiently different from any sequence of contiguous nucleotides selected from the nucleotide sequence encoding human P450RAI-1 (SEQ ID NO:13) that there is no more than about 60% homology between the two sequences when the two sequences are directly aligned with each other. More preferably, the percent homology would be less than about 55%, or less than about 50%, or less than about 45%, or even less than about 40%. Certain probes of the invention are selected so as span borders between introns of the coding sequence as determined from the genomic sequence (SEQ ID NO:3).

The invention includes the method of determining the presence of a nucleic acid molecule encoding P450RAI-2 in a sample containing RNA isolated from a human cell, using such a probe.

In the context of this specification, the term “conserved” describes similarity between sequences. The degree of conservation between two sequences can be determined by optimally aligning the sequences for comparison. Here, sequences were aligned using the Omiga software program, Version 1.13. (Oxford Molecular Group, Inc., Campbell, Calif.). The Omiga software uses the Clustal W Alignment algorithms [Higgins et al., 1989; Higgins et al., 1991; Thompson et al. 19941 Default settings used are as follows: Open gap penalty 10.00; Extend gap penalty 0.05; Delay divergent sequence 40 and Scoring matrix—Gonnet Series. Percent identity or homology between two sequences is determined by comparing a position in the first sequence with a corresponding position in the second sequence. When the compared positions are occupied by the same nucleotide or amino acid, as the case may be, the two sequences are conserved at that position. The degree of conservation between two sequences is often expressed, as it is here, as a percentage representing the ratio of the number of matching positions in the two sequences to the total number of positions compared.

In one particular aspect, the present invention is a nucleic acid molecule of any preceding claim which encodes a protein that is a conservatively substituted variant of the protein encoded by the nucleotide sequence of SEQ ID NO:4.

Further, it will be appreciated that the invention includes nucleic acid molecules comprising nucleic acid sequences having substantial sequence homology with the nucleic acid sequences as shown in SEQ ID NO. 4, 6, 8-10, 18, or 21-28 and fragments thereof. The term “sequences having substantial sequence homology” means those nucleic acid sequences that have slight or inconsequential sequence variations from these sequences, i.e., the sequences function in substantially the same manner to produce functionally equivalent proteins. The variations may be attributable to local mutations or structural modifications.

Nucleic acid sequences having substantial homology include nucleic acid sequences having at least 85%, preferably 90-95% identity with the nucleic acid sequence as shown in SEQ ID NO: 4, 6, 8-10, 18, or 21-28. However, the invention is not to be restricted by this homology, for instance, nucleic acid sequences having at least a 50% homology with the sequence shown in 4, 6, 8-10, 18, or 21-28 are also encompassed within the scope of the present invention.

“Stringent hybridization conditions” is a term known to a person skilled in the art. Appropriate stringency conditions which promote nucleic acid hybridization, for example, 6× sodium chloride/sodium citrate (SSC) at about 45° C. are know. The following examples are found in Current Protocols in Molecular Biology, John Wiley & Sons, NY (1989), 6.3.1-6.3.6: For 50 ml of a first suitable hybridization solution, mix together 24 ml formamide, 12 ml 20×SSC, 0.5 ml 2 M Tris-HCl pH 7.6, 0.5 ml 100× Denhardt's solution, 2.5 ml deionized H₂O, 10 ml 50% dextran sulfate, and 0.5 ml 10% SDS. A second suitable hybridization solution can be 1% crystalline BSA (fraction V), 1 mM EDTA, 0.5 M Na₂HPO₄ pH 7.2, 7% SDS. The salt concentration in the wash step can be selected from a low stringency of about 2×SSC at 50° C. to a high stringency of about 0.2×SSC at 50° C. Both of these wash solutions may contain 0.1% SDS. In addition, the temperature in the wash step can be increased from low stringency conditions at room temperature, about 22° C., to high stringency conditions, at about 65° C. The cited reference gives more detail, but appropriate wash stringency depends on degree of homology and length of probe. If homology is 100%, a high temperature (65° C. to 75° C.) may be used. If homology is low, lower wash temperatures must be used. However, if the probe is very short (<100 bp), lower temperatures must be used even with 100% homology. In general, one starts washing at low temperatures (37° C. to 40° C.), and raises the temperature by 3-5° C. intervals until background is low enough not to be a major factor in autoradiography.

Isolated nucleic acid molecules having sequences which differ from the nucleic acid sequence shown in SEQ ID NO: 4, 6, 8-10, 18, or 21-28 due to degeneracy in the genetic code are also within the scope of the invention. Such nucleic acids encode functionally equivalent proteins but differ in sequence from the above mentioned sequences due to degeneracy in the genetic code.

An isolated nucleic acid molecule of the invention which comprises DNA can be isolated by preparing a labelled nucleic acid probe based on all or part of the nucleic acid sequences as shown in SEQ ID NO: 4, 6, 8-10, 18, or 21-28 and using this labelled nucleic acid probe to screen an appropriate DNA library (e.g. a cDNA or genomic DNA library). For example, a genomic library isolated can be used to isolate a DNA encoding a novel protein of the invention by screening the library with the labelled probe using standard techniques. Nucleic acids isolated by screening of a cDNA or genomic DNA library can be sequenced by standard techniques.

An isolated nucleic acid molecule of the invention which is DNA can also be isolated by selectively amplifying a nucleic acid encoding a novel protein of the invention using the polymerase chain reaction (PCR) methods and cDNA or genomic DNA. It is possible to design synthetic oligonucleotide primers from the nucleic acid sequence as shown in SEQ ID NO: 4, 6, 8-10, 18, or 21-28 for use in PCR. A nucleic acid can be amplified from cDNA or genomic DNA using these oligonucleotide primers and standard PCR amplification techniques. The nucleic acid so amplified can be cloned into an appropriate vector and characterized by DNA sequence analysis. It will be appreciated that cDNA may be prepared from mRNA, by isolating total cellular mRNA by a variety of techniques, for example, by using the guanidinium-thiocyanate extraction procedure of Chirgwin et al., Biochemistry, 18, 5294 5299 (1979). cDNA is then synthesized from the mRNA using reverse transcriptase (for example, Moloney MLV reverse transcriptase available from Gibco/BRL, Bethesda, Md., or AMV reverse transcriptase available from Seikagaku America, Inc., St. Petersburg, Fla.).

An isolated nucleic acid molecule of the invention which is RNA can be isolated by cloning a cDNA encoding a novel protein of the invention into an appropriate vector which allows for transcription of the cDNA to produce an RNA molecule which encodes a protein of the invention. For example, a cDNA can be cloned downstream of a bacteriophage promoter, (e.g., a T7 promoter) in a vector, cDNA can be transcribed in vitro with T7 polymerase, and the resultant RNA can be isolated by standard techniques.

A nucleic acid molecule of the invention may also be chemically synthesized using standard techniques. Various methods of chemically synthesizing polydeoxynucleotides are known, including solid-phase synthesis which, like peptide synthesis, has been fully automated in commercially available DNA synthesizers (See e.g., Itakura et al. U.S. Pat. No. 4,598,049; Caruthers et al. U.S. Pat. No. 4,458,066; and Itakura U.S. Pat. Nos. 4,401,796 and 4,373,071).

Determination of whether a particular nucleic acid molecule encodes a novel protein of the invention may be accomplished by expressing the cDNA in an appropriate host cell by standard techniques, and testing the activity of the protein using the methods as described herein. A cDNA having the activity of a novel protein of the invention so isolated can be sequenced by standard techniques, such as dideoxynucleotide chain termination or Maxam-Gilbert chemical sequencing or by automated DNA sequencing, to determine the nucleic acid sequence and the predicted amino acid sequence of the encoded protein.

The initiation codon and untranslated sequences of nucleic acid molecules of the invention may be determined using currently available computer software designed for the purpose, such as PC/Gene (IntelliGenetics Inc., Calif.). Regulatory elements can be identified using conventional techniques. The function of the elements can be confirmed by using these elements to express a reporter gene which is operatively linked to the elements. These constructs may be introduced into cultured cells using standard procedures. In addition to identifying regulatory elements in DNA, such constructs may also be used to identify proteins interacting with the elements, using techniques known in the art.

The sequence of a nucleic acid molecule of the invention may be inverted relative to its normal presentation for transcription to produce an antisense nucleic acid molecule. The term “antisense” nucleic acid molecule is a nucleotide sequence that is complementary to its target. Preferably, an antisense sequence is constructed by inverting a region preceding or targeting the initiation codon or an unconserved region. In another embodiment the antisense sequence targets all or part of the mRNA or cDNA of P450RAI-2. In particular, the nucleic acid sequences contained in the nucleic acid molecules of the invention or a fragment thereof may be inverted relative to its normal presentation for transcription to produce antisense nucleic acid molecules. In one embodiment the antisense molecules can be used to inhibit P450RAI-2 expression and/or RA metabolism,

The antisense nucleic acid molecules of the invention or a fragment thereof, may be chemically synthesized using naturally occurring nucleotides or variously modified nucleotides designed to increase the biological stability of the molecules or to increase the physical stability of the duplex formed with mRNA or the native gene e.g. phosphorothioate derivatives and acridine substituted nucleotides. The antisense sequences may be produced biologically using an expression vector introduced into cells in the form of a recombinant plasmid, phagemid or attenuated virus in which antisense sequences are produced under the control of a high efficiency regulatory region, the activity of which may be determined by the cell type into which the vector is introduced.

The invention also provides nucleic acids encoding fusion proteins comprising a novel protein of the invention and a selected protein, or a selectable marker protein (see below).

II. Polypeptides of the Invention

The invention further contemplates an isolated P450RAI-2 protein. In an embodiment of the invention, an isolated protein is provided which has the human amino acid sequence as shown in SEQ ID NO:5 or a fragment, preferably biologically active fragment, thereof. The present invention also encompasses peptides encoded by the nucleic acid sequence of SEQ ID NO: 4 and all embodiments therefor as described in reference to the peptides in SEQ ID NO. 5 described below.

Within the context of the present invention, a protein of the invention may in one embodiment include various structural forms of the primary protein which retain biological activity of the cytochrome P450RAI-2. For example, a protein of the invention may be in the form of acidic or basic salts or in neutral form. In addition, individual amino acid residues may be modified by oxidation or reduction. The biological activity of a active cytochrome P450RAI-2 is the ability to oxidize a retinoid. Such activity can be tested for as described herein.

In addition to the full length amino acid sequence (SEQ ID NO: 5), the proteins of the present invention may also include truncations of the proteins, and analogs, and homologs of the proteins and truncations thereof as described herein. Truncated proteins may comprise peptides of at least 10 and preferably at least fourteen amino acid residues.

In one embodiment, the invention provides a peptide fragment of human SEQ ID NO: 5. In another embodiment the invention provides a peptide having an amino acid sequence of the partial mouse P450RAI-2 sequence, SEQ ID NO: 11 or Zebrafish sequence (SEQ ID NO: 12). In another embodiment the invention provides a peptide encoded by any of the nucleic acid molecules of the invention as described above. In yet another embodiment the invention provides an antigenic immunogenic fragment of the proteins of the invention.

Analogs of the proteins having the amino acid sequences shown in SEQ ID NO: 5 and/or truncations thereof as described herein, may include, but are not limited to an amino acid sequence containing one or more amino acid substitutions, insertions, and/or deletions. Amino acid substitutions may be of a conserved or non-conserved nature. Conserved amino acid substitutions involve replacing one or more amino acids of the proteins of the invention with amino acids of similar charge, size, and/or hydrophobicity characteristics. When only conserved substitutions are made the resulting analog should be functionally equivalent. Non-conserved substitutions involve replacing one or more amino acids of the amino acid sequence with one or more amino acids which possess dissimilar charge, size, and/or hydrophobicity characteristics.

Without the intention of being limited thereby, in one embodiment it is preferable that substitutions of amino acids are made that preserve the structure responsible for retinoid metabolizing activity of the proteins disclosed herein. Conservative substitutions are described in the patent literature, as for example, in U.S. Pat. No. 5,264,558. It is thus expected, for example, that interchange among non-polar aliphatic neutral amino acids, glycine, alanine, proline, valine and isoleucine, would be possible. Likewise, substitutions among the polar aliphatic neutral amino acids, serine, threonine, methionine, asparagine and glutamine could possibly be made. Substitutions among the charged acidic amino acids, aspartic acid and glutamic acid, could probably be made, as could substitutions among the charged basic amino acids, lysine and arginine. Substitutions among the aromatic amino acids, including phenylalanine, histidine, tryptophan and tyrosine would also likely be possible. These sorts of substitutions and interchanges are well known to those skilled in the art. Other substitutions might well be possible. Of course, it would also be expected that the greater the percentage of homology, i.e., sequence similarity, of a variant protein with a naturally occurring protein, the greater the retention of metabolic activity. Of course, as protein variants having the activity of P450RAI-2 as described herein are intended to be within the scope of this invention, so are nucleic acids encoding such variants.

One or more amino acid insertions may be introduced into the amino acid sequences shown in SEQ ID NO: 5. Amino acid insertions may consist of single amino acid residues or sequential amino acids ranging from 2 to 15 amino acids in length. For example, amino acid insertions may be used to destroy target sequences so that the protein is no longer active. This procedure may be used in vivo to inhibit the activity of a protein of the invention.

Deletions may consist of the removal of one or more amino acids, or discrete portions from the amino acid sequence shown in SEQ ID NO: 5. The deleted amino acids may or may not be contiguous. The lower limit length of the resulting analog with a deletion mutation is about 10 amino acids, preferably 100 amino acids.

Analogs of the proteins of the invention may be prepared by introducing mutations in the nucleotide sequence encoding the protein. Mutations in nucleotide sequences constructed for expression of analogs of a protein of the invention must preserve the reading frame of the coding sequences. Furthermore, the mutations will preferably not create complementary regions that could hybridize to produce secondary mRNA structures, such as loops or hairpins, which could adversely affect translation of the mRNA.

Mutations may be introduced at particular loci by synthesizing oligonucleotides containing a mutant sequence, flanked by restriction sites enabling ligation to fragments of the native sequence. Following ligation, the resulting reconstructed sequence encodes an analog having the desired amino acid insertion, substitution, or deletion.

Alternatively, oligonucleotide-directed site specific mutagenesis procedures may be employed to provide an altered gene having particular codons altered according to the substitution, deletion, or insertion required. Deletion or truncation of a protein of the invention may also be constructed by utilizing convenient restriction endonuclease sites adjacent to the desired deletion. Subsequent to restriction, overhangs may be filled in, and the DNA religated. Exemplary methods of making the alterations set forth above are disclosed by Sambrook et al (Molecular Cloning: A Laboratory Manual, 2nd Ed., Cold Spring Harbor Laboratory Press, 1989).

Insertions, deletions or substitution mutations of P450RAI-2 can be used to generate dominant negative forms of P450RAI-2 that can act as transdominant repressors of P450RAI-2 activity.

The proteins of the invention also include homologs of the amino acid sequence shown in SEQ ID NO: 5 and/or truncations thereof as described herein. Such homologs are proteins whose amino acid sequences are encoded by nucleic acid sequences that hybridize under stringent hybridization conditions (see discussion of stringent hybridization conditions herein) with a probe used to obtain a protein of the invention. Homologs of a protein of the invention will have the same regions which are characteristic of the protein.

A homologous protein includes a protein with an amino acid sequence having at least 60%, preferably at least 76%, preferably 80-90% identity with the amino acid sequence as shown in SEQ ID NO: 5.

The invention also contemplates isoforms of the proteins of the invention. An isoform contains the same number and kinds of amino acids as a protein of the invention, but the isoform has a different molecular structure. The isoforms contemplated by the present invention are those having the same properties as a protein of the invention as described herein.

The present invention also includes a protein of the invention conjugated with a selected protein, or a selectable marker protein (see below) to produce fusion proteins. Additionally, immunogenic portions of a protein of the invention are within the scope of the invention. Immunogenic portions of a protein is that portion that if administered to a patient can induce an immune response and preferably an antibody response.

A further advantage may be obtained through chimeric forms of the protein, as known in the art. A DNA sequence encoding the entire protein, or a portion of the protein, could thus be linked, for example, with a sequence coding for the C-terminal portion of E. coli β-galactosidase to produce a fusion protein. GST-P450RAI-2 fusion proteins are described in the above examples. An expression system for human respiratory syncytial virus glycoproteins F and G is described in U.S. Pat. No. 5,288,630 issued Feb. 22, 1994 and references cited therein, for example.

The proteins of the invention (including truncations, analogs, etc.) may be prepared using recombinant DNA methods. These proteins may be purified and/or isolated to various degrees using techniques known in the art. Accordingly, nucleic acid molecules of the present invention having a sequence which encodes a protein of the invention may be incorporated according to procedures known in the art into an appropriate expression vector which ensures good expression of the protein. Possible expression vectors include but are not limited to cosmids, plasmids, or modified viruses (e.g., replication defective retroviruses, adenoviruses and adeno-associated viruses), so long as the vector is compatible with the host cell used. The expression “vectors suitable for transformation of a host cell”, means that the expression vectors contain a nucleic acid molecule of the invention and regulatory sequences, selected on the basis of the host cells to be used for expression, which are operatively linked to the nucleic acid molecule. “Operatively linked” is intended to mean that the nucleic acid is linked to regulatory sequences in a manner which allows expression of the nucleic acid.

The invention therefore contemplates a recombinant expression vector of the invention containing a nucleic acid molecule of the invention, or a fragment thereof, and the necessary regulatory sequences for the transcription and translation of the inserted protein-sequence. Suitable regulatory sequences may be derived from a variety of sources, including bacterial, fungal, or viral genes (For example, see the regulatory sequences described in Goeddel, Gene Expression Technology: Methods in Enzymology 185, Academic Press, San Diego, Calif. (1990). Selection of appropriate regulatory sequences is dependent on the host cell chosen, and may be readily accomplished by one of ordinary skill in the art. Examples of such regulatory sequences include: a transcriptional promoter and enhancer or RNA polymerase binding sequence, a ribosomal binding sequence, including a translation initiation signal. Additionally, depending on the host cell chosen and the vector employed, other sequences, such as an origin of replication, additional DNA restriction sites, enhancers, and sequences conferring inducibility of transcription may be incorporated into the expression vector. It will also be appreciated that the necessary regulatory sequences may be supplied by the native protein and/or its flanking regions.

The invention further provides a recombinant expression vector comprising a DNA nucleic acid molecule of the invention cloned into the expression vector in an antisense orientation. That is, the DNA molecule is operatively linked to a regulatory sequence in a manner which allows for expression, by transcription of the DNA molecule, of an RNA molecule which is antisense to a nucleotide sequence of the invention preferably comprising the nucleotides as shown in SEQ ID NO: 4 or fragments thereof. Regulatory sequences operatively linked to the antisense nucleic acid can be chosen which direct the continuous expression of the antisense RNA molecule.

The recombinant expression vectors of the invention may also contain a selectable marker gene that facilitates the selection of host cells transformed or transfected with a recombinant molecule of the invention. Examples of selectable marker genes are genes encoding a protein which confers resistance to certain drugs, such as G418 and hygromycin. Examples of other markers which can be used are: green fluorescent protein (GFP), β-galactosidase, chloramphenicol acetyltransferase, or firefly luciferase. Transcription of the selectable marker gene is monitored by changes in the concentration of the selectable marker protein such as β-galactosidase, chloramphenicol acetyltransferase, or firefly luciferase. If the selectable marker gene encodes a protein conferring antibiotic resistance such as neomycin resistance transformant cells can be selected with G418. Cells that have incorporated the selectable marker gene will survive, while the other cells die. This makes it possible to visualize and assay for expression of recombinant expression vectors of the invention and in particular to determine the effect of a mutation on expression and phenotype. It will be appreciated that selectable markers can be introduced on a separate vector from the nucleic acid of interest.

The recombinant expression or cloning vectors of the invention may also contain genes which encode a fusion moiety which provides increased expression of the recombinant protein; increased solubility of the recombinant protein; and aid in the purification of a target recombinant protein by acting as a ligand in affinity purification. For example, a proteolytic cleavage site may be added to the target recombinant protein to allow separation of the recombinant protein from the fusion moiety subsequent to purification of the fusion protein.

Recombinant expression vectors can be introduced into host cells to produce a transformed host cell. The term “transformed host cell” is intended to include prokaryotic and eukaryotic cells which have been transformed or transfected with a recombinant expression vector of the invention. The terms “transformed with”, “transfected with”, “transformation” and “transfection” are intended to encompass introduction of nucleic acid (e.g. a vector) into a cell by one of many possible techniques known in the art. Prokaryotic cells can be transformed with nucleic acid by, for example, electroporation or calcium chloride mediated transformation. Nucleic acid can be introduced into mammalian cells via conventional techniques such as calcium phosphate or calcium chloride co precipitation, DEAE-dextran-mediated transfection, lipofectin, electroporation or microinjection. Suitable methods for transforming and transfecting host cells can be found in Sambrook et al. (Molecular Cloning: A Laboratory Manual, 2nd Edition, Cold Spring Harbor Laboratory press (1989)), and other such laboratory textbooks.

Suitable host cells include a wide variety of prokaryotic and eukaryotic host cells. For example, the proteins of the invention may be expressed in bacterial cells such as E. coli, insect cells (using baculovirus), yeast cells or mammalian cells, COSI cells. Other suitable host cells can be found in Goeddel, Gene Expression Technology: Methods in Enzymology 185, Academic Press, San Diego, Calif. (1991).

The invention includes a microbial cell that contains and is capable of expressing a heterologous a nucleic acid molecule having a nucleotide sequence as broadly encompassed by the invention. The heterologous nucleic acid molecule can be DNA.

Isolated DNA of the invention can be contained in a recombinant cloning vector.

The invention includes a stably transfected cell line which expresses any one or more proteins as broadly defined by the invention.

The invention includes a culture of cells transformed with a recombinant DNA molecule having a nucleotide sequence as broadly encompassed by the invention. Such a culture of cells can be eukaryotic. They can be piscine—particularly zebrafish, mammalian—particularly human, rat or mouse, for example.

The invention is also a process for producing any protein as broadly defined by the invention. The process includes such steps as:

-   -   preparing a DNA fragment including a nucleotide sequence which         encodes said protein;     -   incorporating the DNA fragment into an expression vector to         obtain a recombinant DNA molecule which includes the DNA         fragment and is capable of undergoing replication;     -   transforming a host cell with said recombinant DNA molecule to         produce a transformant which can express said protein;     -   culturing the transformant to produce said protein; and     -   recovering said protein from resulting cultured mixture.

More particularly, the invention provides a method of preparing a purified protein of the invention comprising introducing into a host cell a recombinant nucleic acid encoding the protein, allowing the protein to be expressed in the host cell and isolating and purifying the protein. Preferably, the recombinant nucleic acid is a recombinant expression vector. Proteins can be isolated from a host cell expressing the protein and purified according to standard procedures of the art, including ammonium sulfate precipitation, column chromatography (e.g. ion exchange, gel filtration, affinity chromatography, etc.), electrophoresis, and ultimately, crystallization [see generally, “Enzyme Purification and Related Techniques”, Methods in Enzymology, 22, 233-577 (1971)].

Alternatively, the protein or parts thereof can be prepared by chemical synthesis using techniques well known in the chemistry of proteins such as solid phase synthesis [Merrifield 1964] or synthesis in homogeneous solution [Houbenwycl, 1987].

III. Applications

1. Diagnostic Applications

The above nucleic acid and peptide molecules of the invention can be used to diagnose a disease affected by P450RAI-2 expression, such as a disease or medical condition associated with or where RA, P450RAI-2 or inhibitors thereof treatment may be indicated. Examples of such conditions have been outlined herein, such as diseases associated with angiogenesis the regulation of the cell cycle or apoptosis, such as cancer, dysplasia, various autoimmune diseases. Determination of peptide or nucleic acid expression levels could assist not only in identifying a medical condition but in determining the appropriate course of treatment.

(i) Nucleic Acids

The above described nucleic acid molecules of the invention, allow those skilled in the art to construct nucleotide probes for use in the detection of nucleotide sequences homologous to P450RAI-2 or a fragment thereof in a sample.

Accordingly, the present invention also relates to a method of detecting the presence of nucleic acid molecules encoding a P450RAI-2 in a sample comprising contacting the sample under hybridization conditions with one or more nucleotide probes which hybridize to the nucleic acid molecules and are labelled with a detectable marker, and, determining the degree of hybridization between the nucleic acid molecule in the sample and the nucleotide probe(s).

A nucleotide probe may be labelled with a detectable marker such as a radioactive label which provides for an adequate signal and has sufficient half life such as 32P, 3H, 14C or the like. Other detectable markers which may be used include antigens that are recognized by a specific labelled antibody, fluorescent compounds, enzymes, antibodies specific for a labelled antigen, and chemiluminescent compounds. An appropriate label may be selected having regard to the rate of hybridization and binding of the probe to the nucleotide to be detected and the amount of nucleotide available for hybridization.

Hybridization conditions which may be used in methods of the invention are known in the art and are described for example in Sambrook J, Fritch E F, Maniatis T. In: Molecular Cloning, A Laboratory Manual, 1989. (Nolan C, Ed.), Cold Spring Harbor Laboratory Press, Cold Spring Harbor, N.Y. The hybridization product may be assayed using techniques known in the art. The nucleotide probe may be labelled with a detectable marker as described herein and the hybridization product may be assayed by detecting the detectable marker or the detectable change produced by the detectable marker.

A nucleic acid molecule of the invention also permits the identification and isolation, or synthesis of nucleotide sequences which may be used as primers to amplify a nucleic acid molecule of the invention, for example, in a polymerase chain reaction (PCR) which is discussed in more detail below. The primers may be used to amplify the genomic DNA or mRNA of other P450RAI-2 genes or coding sequences. The PCR amplified sequences can be examined to determine the relationship between the various P450RAI-2 genes.

The length and bases of primers for use in a PCR are selected so that they will hybridize to different strands of the desired sequence and at relative positions along the sequence such that an extension product synthesized from one primer when it is separated from its template can serve as a template for extension of the other primer into a nucleic acid of defined length. Primers which may be used in the invention are oligonucleotides, i.e., molecules containing two or more deoxyribonucleotides of the nucleic acid molecule of the invention which occur naturally as in a purified restriction endonuclease digest or are produced synthetically using techniques known in the art such as for example phosphotriester and phosphodiester methods (See Good et al. Nucl. Acid Res 4:2157, 1977) or automated techniques (See for example, Conolly, B. A. Nucleic Acids Res. 15:15(7): 3131, 1987). The primers are capable of acting as a point of initiation of synthesis when placed under conditions which permit the synthesis of a primer extension product which is complementary to a DNA sequence of the invention, i.e., in the presence of nucleotide substrates, an agent for polymerization such as DNA polymerase and at suitable temperature and pH. Preferably, the primers are sequences that do not form secondary structures by base pairing with other copies of the primer or sequences that form a hair pin configuration. The primer preferably contains between about 7 and 25 nucleotides.

The primers may be labelled with detectable markers which allow for detection of the amplified products. Suitable detectable markers are radioactive markers such as P-32, S-35, I-125, and H-3, luminescent markers such as chemiluminescent markers, preferably luminol, and fluorescent markers, preferably dansyl chloride, fluorcein-5-isothiocyanate, and 4-fluor-7-nitrobenz-2-axa-1,3 diazole, enzyme markers such as horseradish peroxidase, alkaline phosphatase, β-galactosidase, acetylcholinesterase, or biotin.

It will be appreciated that the primers may contain non-complementary sequences provided that a sufficient amount of the primer contains a sequence which is complementary to a nucleic acid molecule of the invention or oligonucleotide fragment thereof, which is to be amplified. Restriction site linkers may also be incorporated into the primers allowing for digestion of the amplified products with the appropriate restriction enzymes facilitating cloning and sequencing of the amplified product.

In an embodiment of the invention a method of determining the presence of a nucleic acid molecule having a sequence encoding a protein of the invention is provided comprising treating the sample with primers which are capable of amplifying the nucleic acid molecule or a predetermined oligonucleotide fragment thereof in a polymerase chain reaction to form amplified sequences, under conditions which permit the formation of amplified sequences and, assaying for amplified sequences.

Polymerase chain reaction as used herein refers to a process for amplifying a target nucleic acid sequence as generally described in Innis et al, Academic Press, 1990 in Mullis et al., U.S. Pat. No. 4,863,195 and Mullis, U.S. Pat. No. 4,683,202. Conditions for amplifying a nucleic acid template are described in M. A. Innis and D. H. Gelfand, PCR Protocols, A Guide to Methods and Applications M. A. Innis, D. H. Gelfand, J. J. Sninsky and T. J. White eds, pp3-12, Academic Press 1989.

The amplified products can be isolated and distinguished based on their respective sizes using techniques known in the art. For example, after amplification, a DNA sample can be separated on an agarose gel and visualized, after staining with ethidium bromide, under ultra violet (uv) light. DNA may be amplified to a desired level and a further extension reaction may be performed to incorporate nucleotide derivatives having detectable markers such as radioactive labelled or biotin labelled nucleoside triphosphates. The primers may also be labelled with detectable markers as discussed above. The detectable markers may be analyzed by restriction enzyme digestion and electrophoretic separation or other techniques known in the art.

Conditions which may be employed in the methods of the invention using PCR are those which permit hybridization and amplification reactions to proceed in the presence of DNA in a sample and appropriate complementary hybridization primers. Conditions suitable for a polymerase chain reaction are generally known in the art. For example, see M. A. Innis and D. H. Gelfand, PCR Protocols, A guide to Methods and Applications M. A. Innis, D. H. Gelfand, J. J. Sninsky and T. J. White eds, pp3-12, Academic Press 1989. To amplify DNA template strands, preferably, the PCR utilizes polymerase obtained from the thermophilic bacterium Thermus aquatics (Taq polymerase, GeneAmp Kit, Perkin Elmer Cetus) or other thermostable polymerase.

It will be appreciated that other techniques such as the Ligase Chain Reaction (LCR) and NASBA may be used to amplify a nucleic acid molecule of the invention (Barney in “PCR Methods and Applications”, August 1991, Vol. 1(1), page 5, and European Published Application No. 0320308, published Jun. 14, 1989, and U.S. Pat. No. 5,130,238 to Malek).

(ii) Antibodies

A P450RAI-2 protein of the invention or antigenic portion thereof can be used to prepare antibodies specific for the proteins of the invention, preferably to a protein having SEQ ID NO: 5 or partial sequence SEQ ID NO: 11 or 12. Antibodies can be prepared which bind a distinct epitope in an unconserved region of the protein. An unconserved region of the protein is one which does not have substantial sequence homology to other proteins. Alternatively, a region from a well-characterized domain can be used to prepare an antibody to a conserved region of a protein of the invention. Antibodies having specificity for a protein of the invention may also be raised from fusion proteins.

Conventional methods can be used to prepare the antibodies. For example, by using a peptide of a protein of the invention, polyclonal antisera or monoclonal antibodies can be made using standard methods. A mammal, (e.g., a mouse, hamster, or rabbit) can be immunized with an immunogenic form of the peptide which elicits an antibody response in the mammal. Techniques for conferring immunogenicity on a peptide include conjugation to carriers or other techniques well known in the art. For example, the peptide can be administered in the presence of adjuvant. The progress of immunization can be monitored by detection of antibody titers in plasma or serum. Standard ELISA or other immunoassay procedures can be used with the immunogen as antigen to assess the levels of antibodies. Following immunization, antisera can be obtained and, if desired, polyclonal antibodies isolated from the sera.

To produce monoclonal antibodies, antibody producing cells (lymphocytes) can be harvested from an immunized animal and fused with myeloma cells by standard somatic cell fusion procedures thus immortalizing these cells and yielding hybridoma cells. Such techniques are well known in the art, (e.g., the hybridoma technique originally developed by Kohler and Milstein (Nature 256, 495-497 (1975)) as well as other techniques such as the human B-cell hybridoma technique (Kozbor et al., Immunol. Today 4, 72 (1983)); the EBV-hybridoma technique to produce human monoclonal antibodies (Cole et al. Monoclonal Antibodies in Cancer Therapy (1985) Allen R. Bliss, Inc., pages 77-96); and screening of combinatorial antibody libraries (Huse et al., Science 246, 1275 (1989)). Hybridoma cells can be screened immunochemically for production of antibodies specifically reactive with the peptide and the monoclonal antibodies can be isolated. Therefore, the invention also contemplates hybridoma cells secreting monoclonal antibodies with specificity for a protein of the invention.

The term “antibody” as used herein is intended to include fragments thereof which also specifically react with, a protein of the invention, or peptide thereof. Antibodies can be fragmented using conventional techniques and the fragments screened for utility in the same manner as described above. For example, F(ab′)2 fragments can be generated by treating antibody with pepsin. The resulting F(ab′)2 fragment can be treated to reduce disulfide bridges to produce Fab′ fragments.

Chimeric antibody derivatives, i.e., antibody molecules that combine a non-human animal variable region and a human constant region are also contemplated within the scope of the invention. Chimeric antibody molecules can include, for example, the antigen binding domain from an antibody of a mouse, rat, or other species, with human constant regions. Conventional methods may be used to make chimeric antibodies containing the immunoglobulin variable region which recognizes a P450RAI-2 protein of the invention (See, for example, Morrison et al., Proc. Natl. Acad. Sci. U.S.A. 81,6851 (1985); Takeda et al., Nature 314, 452 (1985), Cabilly et al., U.S. Pat. No. 4,816,567; Boss et al., U.S. Pat. No. 4,816,397; Tanaguchi et al., European Patent Publication EP171496; European Patent Publication 0173494, United Kingdom patent GB 2177096B).

Monoclonal or chimeric antibodies specifically reactive with a protein of the invention as described herein can be further humanized by producing human constant region chimeras, in which parts of the variable regions, particularly the conserved framework regions of the antigen-binding domain, are of human origin and only the hypervariable regions are of non-human origin. Such immunoglobulin molecules may be made by techniques known in the art (e.g., Teng et al., Proc. Natl. Acad. Sci. U.S.A., 80, 7308-7312 (1983); Kozbor et al., Immunology Today, 4, 7279 (1983); Olsson et al., Meth. Enzymol., 92, 3-16 (1982); and PCT Publication WO92/06193 or EP 0239400). Humanized antibodies can also be commercially produced (Scotgen Limited, 2 Holly Road, Twickenham, Middlesex, Great Britain.)

Specific antibodies, or antibody fragments reactive against a protein of the invention may also be generated by screening expression libraries encoding immunoglobulin genes, or portions thereof, expressed in bacteria with peptides produced from nucleic acid molecules of the present invention. For example, complete Fab fragments, VH regions and FV regions can be expressed in bacteria using phage expression libraries (See for example Ward et al., Nature 341, 544-546: (1989); Huse et al., Science 246, 1275-1281 (1989); and McCafferty et al. Nature 348, 552-554 (1990)).

The antibodies may be labelled with a detectable marker including various enzymes, fluorescent materials, luminescent materials and radioactive materials. Examples of suitable enzymes include horseradish peroxidase, alkaline phosphatase, β-galactosidase, or acetylcholinesterase; examples of suitable fluorescent materials include umbelliferone, fluorescein, fluorescein isothiocyanate, rhodamine, dichlorotriazinylamine fluorescein, dansyl chloride or phycoerythrin; an example of a luminescent material includes luminol; and examples of suitable radioactive material include S-35, Cu-64, Ga-67, Zr-89, Ru-97, Tc-99m, Rh-105, Pd-109, In-111, I-123, I-125, I-131, Re-186, Au-198, Au-199, Pb-203, At-211, Pb-212 and Bi-212. The antibodies may also be labelled or conjugated to one partner of a ligand binding pair. Representative examples include avidin-biotin and riboflavin-riboflavin binding protein. Methods for conjugating or labelling the antibodies discussed above with the representative labels set forth above may be readily accomplished using conventional techniques.

Antibodies reactive against P450RAI-2 proteins of the invention (e.g., enzyme conjugates or labelled derivatives) may be used to detect a protein of the invention in various samples, for example they may be used in any known immunoassays which rely on the binding interaction between an antigenic determinant of a protein of the invention and the antibodies. Examples of such assays are radioimmunoassays, western immunoblotting, enzyme immunoassays (e.g., ELISA), immunofluorescence, immunoprecipitation, latex agglutination, hemagglutination, and histochemical tests. Thus, the antibodies may be used to identify or quantify the amount of a protein of the invention in a sample.

A sample may be tested for the presence or absence of a P450RAI-2 by contacting the sample with an antibody specific for an epitope of a P450RAI-2 protein which antibody is capable of being detected after it becomes bound to a P450RAI-2 protein in the sample, and assaying for antibody bound to a P450RAI-2 protein in the sample, or unreacted antibody.

In a method of the invention a predetermined amount of a sample or concentrated sample is mixed with antibody or labelled antibody. The amount of antibody used in the method is dependent upon the labelling agent chosen. The resulting protein bound to antibody or labelled antibody may be isolated by conventional isolation techniques, for example, salting out, chromatography, electrophoresis, gel filtration, fractionation, absorption, polyacrylamide gel electrophoresis, agglutination, or combinations thereof.

The sample or antibody may be insolubilized, for example, the sample or antibody can be reacted using known methods with a suitable carrier. Examples of suitable carriers are Sepharose or agarose beads. When an insolubilized sample or antibody is used protein bound to antibody or unreacted antibody is isolated by washing. For example, when the sample is blotted onto a nitrocellulose membrane, the antibody bound to a protein of the invention is separated from the unreacted antibody by washing with a buffer, for example, phosphate buffered saline (PBS) with bovine serum albumin (BSA).

When labelled antibody is used, the presence of a P450RAI-2 can be determined by measuring the amount of labelled antibody bound to a protein of the invention in the sample or of the unreacted labelled antibody. The appropriate method of measuring the labelled material is dependent upon the labelling agent.

When unlabelled antibody is used in a method of the invention, the presence of a P450RAI-2 can be determined by measuring the amount of antibody bound to the P450RAI-2 using substances that interact specifically with the antibody to cause agglutination or precipitation. In particular, labelled antibody against an antibody specific for a protein of the invention, can be added to the reaction mixture. The antibody against an antibody specific for a protein of the invention can be prepared and labelled by conventional procedures known in the art which have been described herein. The antibody against an antibody specific for a protein of the invention may be a species specific anti-immunoglobulin antibody or monoclonal antibody, for example, goat anti-rabbit antibody may be used to detect rabbit antibody specific for a protein of the invention.

(iii) Methods Of the Invention

The invention includes a protein of the invention for use in metabolizing retinoic acid in an organism or cell in need of such metabolizing. The invention also includes use of a protein of the invention in the preparation of a medicament for use in metabolizing retinoic acid in an organism. Preferably the protein has sequence of SEQ ID NO: 5.

The invention includes a method for metabolizing retinoic acid, particularly all-trans retinoic acid, in an organism or cell comprising administering a protein as broadly defined by the invention, most preferably of SEQ ID NO: 5.

The invention is also a method for inhibiting retinoic acid hydroxylation in an organism in need of such inhibition, comprising administering to the organism an effective amount of an antisense nucleic acid or oligonucleotide substantially complementary to at least a portion of the sequence identified as SEQ ID NO:4. In such a method, the portion can be at least 5 bases in length, or at least about 10 bases in length, or at least about 15 bases in length, or at least about 20 bases in length, or at least about 25 bases in length, or at least about 30 bases in length, or at least about 35 bases in length, or at least about 40 bases in length, or at least about 45 bases in length, or at least about 50 bases in length. Other inhibitors, of RA metabolism such as antibodies to P450RAI-2, or inhibitors of P450RAI-2 activity could also be used.

A preferred organism to be treated is human but could be any organism with an RA metabolism or P450RAI-2 related condition.

The organism may be being treated for a medical condition or disease wherein RA treatment may be indicated. In one embodiment the disease or medical condition is selected from the group consisting of cancer, angiogenesis, actinic keratosis, oral leukoplakia, a secondary tumor of the head and/or neck, a non-small cell lung carcinoma, a basal cell carcinoma, acute promyelocytic leukemia, skin cancer, and a premalignancy associated actinic keratosis, acne, psoriasis and/or ichthyosis, and particularly, acute promyelocytic leukemia. In another embodiment the peptides and nucleic and molecules of the invention may be used to treat disorders of the brain such as memory loss or learning dificiencies.

In one embodiment the invention includes a kit for determining the presence of a protein as broadly described above, or containing an amino acid sequence as identified by SEQ ID NO:5 (human P450RAI-2) SEQ ID NO:11 (mouse CYP26B) or SEQ ID NO:12 (zebrafish CYB26B), comprising an antibody to the protein linked to a reporter system, wherein the reporter system produces a detectable response when a predetermined amount of the protein and the antibody are bound together. In a preferred aspect, the antibody is specific for a protein that includes the amino acid sequence identified as SEQ ID NO:5.

The invention also includes a kit for determining the presence of a first said nucleic acid molecule as broadly defined by the invention. The kit includes a second nucleic acid molecule capable of hybridizing with at least a portion of a the first nucleic acid molecule under the high stringency conditions of paragraph (a), above, in which the second nucleic acid molecule is linked to a reporter system wherein the reporter system produces a detectable response when a predetermined amount of the first and second molecules are hybridized together. The second nucleic acid molecule can be at least 5 bases in length, or at least about 10 bases in length, or at least about 15 bases in length, or at least about 20 bases in length, or at least about 25 bases in length, or at least about 30 bases in length, or at least about 35 bases in length, or at least about 40 bases in length, or at least about 45 bases in length, or at least about 50 bases in length.

The invention is also a method of screening drugs for their modulating effect on activity of a protein as broadly defined by the invention, which method includes exposing a purified said protein to a said drug and determining the effect on the activity. Usually, the modulating effect would be to inhibit the activity of the protein in question. Typically, the activity of the protein is oxidation, e.g., hydroxylation of a retinoic acid, particularly all-trans retinoic acid. In a preferred embodiment, the activity is oxidation of all-trans retinoic acid and the protein includes the amino identified as SEQ ID NO:5.

The invention also includes a method of screening drugs for their effect on expression of a gene, wherein the gene is an inducible gene containing a nucleotide sequence as broadly defined by the invention, by all-trans retinoic acid. The method includes exposing a eukaryotic cell to a said drug and determining the effect on gene expression. Preferably, the gene includes the nucleotide sequence identified as SEQ ID NO:4.

The cell can be a mammalian cell, particularly, a human cell.

The invention includes any drug identified according to a method of the invention, particularly for a purpose related to its related to its modulating effect on the activity of a protein of the invention.

The invention includes a method for inhibiting retinoic acid metabolism in an organism in need of such inhibition, or in cells obtained from such an organism, comprising administering to the organism an effective amount of a drug of the invention.

The invention includes a method of oxidizing a retinoid. The method includes exposing the retinoid to a protein as broadly defined by the invention, and particularly where the protein includes the amino acid sequence identified as SEQ ID NO:5. The retinoid can be a retinoic acid, particularly, all-trans retinoic acid.

In another aspect, the invention is a method of screening a drug for its activity on a protein. The method includes steps of:

-   -   (i) providing a cell line having heterologous DNA encoding a         functional protein as broadly defined by the invention         incorporated thereinto so as to be capable of expressing said         protein;     -   (ii) exposing the cell line to the drug under conditions in         which said protein is expressed in an active form to expose the         protein to the drug; and     -   (iii) determining the effect of the drug on the activity of the         protein.

The method can include exposing the cell line to a substrate of the protein under conditions in which the protein is expressed in an active form to expose the protein to the substrate.

In a particular aspect, the activity is oxidation.

Step (ii) of the method can include exposing the cell line to the drug and the substrate simultaneously.

The substrate can be a retinoid, particularly, a retinoic acid, more particularly, all-trans retinoic acid.

The oxidative activity can be oxidation of the β-ionone ring of the substrate, particularly, hydroxylation.

According to a particular aspect, the heterologous DNA encodes the protein identified as SEQ ID NO:5.

The invention is also a method for screening an agent for its effect on an activity of a first protein relative to its effect on the activity of a second protein. This method includes steps of:

-   -   (a) providing a first protein, wherein the protein one defined         according this invention;     -   (b) providing a second protein, wherein the second protein is a         cytochrome P450;     -   (c) exposing the first protein to the agent;     -   (d) exposing the second protein to the agent; and     -   (e) determining the effect of the agent on the activity of the         first protein relative to its effect on the activity of the         second protein.

According to the method, the activity of each protein under consideration can be the ability of the proteins to oxidize a retinoid and it optionally limited to the ability to oxidize a retinoid at the 4-position of the β-ionone ring and/or to hydroxylate a retinoid at the 4-position of the β-ionone ring.

The retinoid can be a retinoic acid, and it can simply be all-trans retinoic acid.

The first protein can be a human protein and it can include the sequence identified as SEQ ID NO:5.

The method can be such that the second protein is selected from the group of proteins encoded by: (a) a nucleotide sequence that hybridizes under high stringency conditions, wherein high stringency conditions include a wash step of about 0.2×SSC at 50° C., to the nucleotide sequence shown as SEQ ID NO:13 or SEQ ID NO:14 or SEQ ID NO:17, and encodes a protein that oxidizes a retinoid; and (b) a nucleotide sequence that hybridizes under high stringency conditions, wherein high stringency conditions include a wash step of about 0.2×SSC at 50° C., to the nucleotide sequence shown as SEQ ID NO:13 or SEQ ID NO:14, and encodes a protein that hydroxylates retinoic acid at the 4 position of the β-ionone ring.

The second protein can be a human protein and it can include a protein which includes the amino acid sequence encoded by the nucleotide sequence identified as SEQ ID NO:13.

Step (c) of the method can include exposing the first protein to a retinoid.

Step (d) of the method can include exposing the second protein to a retinoid.

Each of steps (c) and (d) can include exposing the first protein to a retinoid.

Step (c) can include exposing the first protein to said retinoid at various concentrations and/or step (d) can include exposing the second protein to said retinoid at various concentrations.

In another broad aspect, the invention is a method for screening an agent for its effect on an activity of a first protein relative to its effect on the activity of a second protein where the proteins are each expressed in a cell or group of cells. Such method thus includes:

-   -   (a) providing a group of first cells having expressibly         incorporated thereinto heterologous DNA encoding a first protein         wherein the protein is a protein of the invention as defined         herein;     -   (b) providing a group of second cells having expressibly         incorporated thereinto heterologous DNA encoding a second         protein, where the second protein is a cytochrome P450;     -   (c) exposing the first cells to the agent under conditions in         which the first protein is expressed;     -   (d) exposing the second cells to the agent under conditions in         which the second protein is expressed; and     -   (e) determining the effect of the agent on the activity of the         first protein relative to its effect on the activity of the         second protein.

Step (e) of the method can include monitoring the disappearance of the agent in the presence the first cells and monitoring the disappearance of the agent in the presence of the second cells.

Step (e) can include monitoring the appearance of an oxidized product or products formed from the agent on exposure to the first cells and monitoring the appearance of the oxidized product or products formed from the agent on exposure to the second cells.

Step (c) can include exposing the first cells to a substrate of the first protein in the presence of the agent and step (d) can include exposing the second cells to the substrate in the presence of the agent.

Step (e) can include monitoring the production of a reaction product or products formed from the substrate on exposure to the first protein in step (c) and, further, step (e) can include monitoring the production of the reaction product or products formed from the substrate on exposure to the second protein in step (d).

Step (e) can include monitoring reduction in the amount of substrate on exposure to the first protein in step (c) and step (e) can include monitoring the reduction in the amount of the substrate on exposure to the second protein in step (d).

The substrate can be a retinoid, which can be a retinoic acid, which can be all-trans retinoic acid.

The observed activity of each protein can be its ability to oxidize a retinoid, particularly, the ability to oxidize a retinoid at the 4-position of the β-ionone ring, or the ability to hydroxylate a retinoid at the 4-position of the β-ionone ring.

The first protein can be a human protein and it can have the sequence identified as SEQ ID NO:5.

The second protein can be selected from the group of proteins encoded by: (a) a nucleotide sequence that hybridizes under high stringency conditions, wherein high stringency conditions include a wash step of about 0.2×SSC at 50° C., to the nucleotide sequence shown as SEQ ID NO:13 or SEQ ID NO:14, and encodes a protein that oxidizes a retinoid; and (b) a nucleotide sequence that hybridizes under high stringency conditions, wherein high stringency conditions include a wash step of about 0.2×SSC at 50° C., to the nucleotide sequence shown as SEQ ID NO:13 or SEQ ID NO:14, and encodes a protein that hydroxylates retinoic acid at the 4 position of the β-ionone ring.

The second protein can be a human protein and it can include the amino acid sequence encoded by the nucleotide sequence identified as SEQ ID NO:13.

Step (c) of the method can include exposing the first cells to a retinoid.

Step (d) can include exposing the second cells to a retinoid.

Step (c) can include exposing the first cells to said retinoid at various concentrations.

Step (d) can also include exposing the second cells to a retinoid at various concentrations.

In another aspect, the present invention is a method of inducing in an eukaryotic cell, production of RNA comprising the nucleotide sequence identified as SEQ ID NO:4 The method includes the steps of:

-   -   exposing the cell to a retinoid; and     -   hybridizing the RNA with a probe comprising a nucleic acid         molecule comprising a nucleotide sequence which encodes a         protein of the present invention.

The cell can be a mammalian cell, particularly a human cell.

The retinoid can be a retinoic acid, particularly, all-trans retinoic acid.

The nucleic acid sequence can be a non-coding sequence complementary to a coding sequence of a nucleic acid molecule encoding the protein comprising the amino acid sequence identified as SEQ ID NO: 5 and the probe is at least 10 nucleotide residues in length, or the probe is at least 15 nucleotide residues in length, or the probe is at least 20 nucleotide residues in length, or the probe is at least 25 nucleotide residues in length, or the probe is at least 30 nucleotide residues in length, or the probe is at least 35 nucleotide residues in length, or the probe is at least 40 nucleotide residues in length, or the probe is at least 45 nucleotide residues in length, or the probe is at least 50 nucleotide residues in length, or the probe is at least 55 nucleotide residues in length, or the probe is at least 56 nucleotide residues in length, or the probe is at least 60 nucleotide residues in length.

The invention includes a method of inducing expression in an eukaryotic cell, a protein comprising the amino acid sequence identified as SEQ ID NO: 5, the method comprising the steps of:

-   -   exposing the cell to a retinoid in an amount sufficient to         induce said expression; and     -   isolating the protein from the cell.

Isolating the protein can include exposing proteins produced by the cell after said exposure step to an antibody which binds specifically to the desired protein.

In the context of this invention, an antibody which “specifically binds” (and grammatical equivalents) to a protein refers to the phenomenon in which an antibody recognizes and binds to a specific binding entity, e.g., protein, but substantially does not recognize or bind to any other specific binding entity.

The cell can be a mammalian cell, particularly, a human cell.

The retinoid can be a retinoic acid, particularly, all-trans retinoic acid.

Human genomic P450RAI-1 sequences are identified herein as SEQ ID NOs:15 and 16. The mouse sequence encoding P450RAI-1 is identified herein as SEQ ID NO:17.

In another aspect, the present invention includes a fragment of the nucleotide sequence encoding P450RAI-2 (SEQ ID NO:4). Such a fragment can find usefulness as a probe. The complement of the probe can find utility in, for example, manufacture of the probe. In a particular use, the probe can be used to determine the presence of an RNA molecule in a sample which might, or might not, also include an RNA molecule encoding P450RAI-1. Such a probe would generally be 20 nucleotides long or be at least 20 nucleotides long. The probe could also be 25, 30, 35, 40, 45, 50, 55, 60 or more nucleotides in length and the probe can include the full length of the complement to the sequence to which it is intended to bind. The sequence of the probe would also be sufficiently distinguishable from any portion of the sequence encoding P450RAI-1 that it would not cross-hybridize to a significant extent to a nucleotide sequence that encodes P450RAI-1, or portion thereof, particularly to an RNA encoding P450RAI-1. Such a probe would thus be sufficiently different from any sequence of contiguous nucleotides selected from the nucleotide sequence encoding human P450RAI-1 (SEQ ID NO:13) that there is no more than about 60% homology between the two sequences when the two sequences are directly aligned with each other. More preferably, the percent homology would be less than about 55%, or less than about 50%, or less than about 45%, or even less than about 40%. Certain probes of the invention are selected so as span borders between introns of the coding sequence as determined from the genomic sequence (SEQ ID NO:3).

The invention includes the method determining the presence of a nucleic molecule encoding P450RAI-2 in a sample containing RNA isolated from human cell, using such a probe.

In the context of this specification, the term “conserved” describes similarity between sequences. The degree of conservation between two sequences can be determined by optimally aligning the sequences for comparison. Here, sequences were aligned using the Omiga software program, Version 1.13. (Oxford Molecular Group, Inc., Campbell, Calif.). The Omiga software uses the Clustal W Alignment algorithms [Higgins et al., 1989; Higgins et al., 1991; Thompson et al. 1994] Default settings used are as follows: Open gap penalty 10.00; Extend gap penalty 0.05; Delay divergent sequence 40 and Scoring matrix—Gonnet Series. Percent identity or homology between two sequences is determined by comparing a position in the first sequence with a corresponding position in the second sequence. When the compared positions are occupied by the same nucleotide or amino acid, as the case may be, the two sequences are conserved at that position. The degree of conservation between two sequences is often expressed, as it is here, as a percentage representing the ratio of the number of matching positions in the two sequences to the total number of positions compared.

The generic term “retinoids” means a group of compounds which includes retinoic acid, vitamin A (retinol) and a series of natural and synthetic derivatives that can exert profound effects on development and differentiation in a wide variety of systems. For purposes of this disclosure “retinoid” is also intended to encompass an equivalent thereof having the same functional characteristics which may be produced, for example, by computational chemistry.

“Stringent hybridization conditions” takes on its common meaning to a person skilled in the art here. Appropriate stringency conditions which promote nucleic acid hybridization, for example, 6× sodium chloride/sodium citrate (SSC) at about 45° C. are known to those skilled in the art. The following examples are found in Current Protocols in Molecular Biology, John Wiley & Sons, NY (1989), 6.3.1-6.3.6: For 50 ml of a first suitable hybridization solution, mix together 24 ml formamide, 12 ml 20×SSC, 0.5 ml 2 M Tris-HCl pH 7.6, 0.5 ml 100× Denhardt's solution, 2.5 ml deionized H₂O, 10 ml 50% dextran sulfate, and 0.5 ml 10% SDS. A second suitable hybridization solution can be 1% crystalline BSA (fraction V), 1 mM EDTA, 0.5 M Na₂HPO₄ pH 7.2, 7% SDS. The salt concentration in the wash step can be selected from a low stringency of about 2×SSC at 50° C. to a high stringency of about 0.2×SSC at 50° C. Both of these wash solutions may contain 0.1% SDS. In addition, the temperature in the wash step can be increased from low stringency conditions at room temperature, about 22° C., to high stringency conditions, at about 65° C. The cited reference gives more detail, but appropriate wash stringency depends on degree of homology and length of probe. If homology is 100%, a high temperature (65° C. to 75° C.) may be used. If homology is low, lower wash temperatures must be used. However, if the probe is very short (<100bp), lower temperatures must be used even with 100% homology. In general, one starts washing at low temperatures (37° C. to 40° C.), and raises the temperature by 3-5° C. intervals until background is low enough not to be a major factor in autoradiography.

The invention also includes a method of inhibiting retinoic acid hydroxylation in an organism in need of such inhibition by administering to the organism an effective amount of an antibody, such antibodies being described herein. A particularly useful antibody for the treatment of a human would be an antibody to the protein having the amino acid sequence identified as SEQ ID NO:5, or a portion thereof. It would be advantageous to adapt such an antibody for administration to a human by “humanizing” the antibody, as is understood by those skilled in the art [Hozumi, 1993].

(iv) Kits

Reagents suitable for conducting the above described diagnostic and/or methods of the invention may be packaged into convenient kits providing the necessary materials, packaged into suitable containers. Such kits may include all the reagents required to detect P450RAI-2 in a sample by means of the methods described herein, and optionally suitable supports useful in performing the methods of the invention.

In one embodiment of the invention the kit contains a nucleotide probe which hybridizes with a nucleic acid molecule of the invention, reagents required for hybridization of the nucleotide probe with the nucleic acid molecule, and directions for its use. In another embodiment of the invention the kit includes antibodies of the invention and reagents required for binding of the antibody to a P450RAI-2 protein in a sample. In still another embodiment of the invention, the kit includes primers which are capable of amplifying a nucleic acid molecule of the invention or a predetermined oligonucleotide fragment thereof, all the reagents required to produce the amplified nucleic acid molecule or predetermined fragment thereof in the polymerase chain reaction, and means for assaying the amplified sequences.

The methods and kits of the present invention have many practical applications. For example, the methods and kits of the present invention may be used to detect P450RAI-2 in any medical sample suspected of containing or lacking P450RAI-2 and used to diagnose diseases associated with P450RAI-2 or RA, expression or metabolism or where RA, P450RAI-2 inhibitor or P450RAT-2 treatment may be indicated. Examples of such diseases include cancer, dysplasia, certain autoimmune diseases or dermatological disorders, angiogenesis, conditions of high order brain functions or other conditions as noted herein. Samples which may be tested include bodily materials such as blood, urine, serum, tears, saliva, feces, tissues and the like.

Before testing a sample in accordance with the methods described herein, the sample may be concentrated using techniques known in the art, such as centrifugation and filtration. For hybridization and/or PCR-based methods described herein, nucleic acids may be extracted from cell extracts of the test sample using techniques known in the art.

2. Therapeutic Applications

Methods of Treatment/Pharmaceutical Compositions

P450RAI-2 may play a role in a number of diseases, such as those associated with regulation of the cell cycle or apoptosis. In particular P450RAI-2 may play a role in cancer or dysplasia by activating apoptosis. As such, the invention comprises methods for modulating or simulating P450RAI-2 activity or P450RAI-2 expression, preferably for treating or preventing a P450RAI-2 related condition. The invention further comprises uses of the modulating or simulating agents disclosed herein for the preparation of a medicament for treating or preventing a condition associated with P450RAI-2 expression or activity. In another embodiment the invention provides a use of the modulating or simulating agents for the treatment or prevention of a P450RAI-2 related condition.

Accordingly, the present invention provides a method of treating or preventing a disease associated with P450RAI-2 expression or activity comprising administering an agent that modulates or simulates P450RAI-2 expression or activity to an animal in need thereof, such as in an animal with cancer, dysplasia an autoimmune disease, or dermatological.

In a preferred embodiment, preferably such agents stimulate or simulate P450RAI-2 activity. Examples of agents that activate or simulate P450RAI-2 activity would include without limitations, P450RAI-2, the gene encoding for P450RAI-2 with suitable promoters, such promoters preferably being tissue specific promoters and therapeutically effective fragments of the nucleic acid and amino acid sequences of the invention.

Examples of agents that inhibit P450RAI-2 include antisense nucleic acid molecules, antibodies and transdominant inhibitors, as described herein.

Agents that inhibit, activate, or stimulate P450RAI-2 can be formulated into pharmaceutical compositions with or without RA for adminstration to subjects in a biologically compatible form suitable for administration in vivo. As used herein “biologically compatible form suitable for administration in vivo” means a form of the substance to be administered in which therapeutic effects outweigh any toxic effects. The substances may be administered to animals in need thereof. Animals, as used herein refers to any animal susceptible to a disease associated with P450RAI-2 expression preferably dogs, cats, mice, horses and humans.

Administration of an “effective amount” of pharmaceutical compositions of the present invention is defined as an amount of the pharmaceutical composition, at dosages and for periods of time necessary to achieve the desired result. For example, a therapeutically active amount of a substance may vary according to factors such as disease state, age, sex, and weight of the recipient, and the ability of the substance to elicit a desired response in the recipient. Dosage regima may be adjusted to provide an optimum Therapeutic response. For example, several divided doses may be administered daily or the dose may be proportionally reduced as indicated by the exigencies of the therapeutic situation.

An active substance may be administered in a convenient manner such as by injection (subcutaneous, intravenous, topical, intratumoral etc.), oral administration, inhalation, transdermal application, or rectal administration. Depending on the route of administration, the active substance may be coated in a material to protect the compound from the action of enzymes, acids and other natural conditions which may inactivate the compound.

The compositions described herein can be prepared by known methods for the preparation of pharmaceutically acceptable compositions which can be administered to subjects, such that an effective quantity of the active substance is combined in a mixture with a pharmaceutically acceptable vehicle. Suitable vehicles are described, for example, in Remington's Pharmaceutical Sciences (Remington's Pharmaceutical Sciences, Mack Publishing Company, Easton, Pa., USA 1985). On this basis, the compositions include, albeit not exclusively, solutions of the substances in association with one or more pharmaceutically acceptable vehicles or diluents, and contained in buffered solutions with a suitable pH and iso-osmotic with the physiological fluids.

Recombinant nucleic acid molecules comprising a sense, an antisense sequence or oligonucleotide fragment thereof, may be directly introduced into cells or tissues in vivo using delivery vehicles known in the art such as retroviral vectors, adenoviral vectors and DNA virus vectors. They may also be introduced into cells in vivo using physical techniques known in the art such as microinjection and electroporation or chemical methods such as coprecipitation and incorporation of DNA into liposomes. Recombinant molecules may also be delivered in the form of an aerosol or by lavage.

The utility of the substances, antibodies, sense and antisense nucleic acid molecules, and compositions of the invention may be confirmed in animal experimental model systems. Suitable animal model systems which can be used to determine P450RAI-2 activity may include, but is not limited or P450RAI-2 knock-out transgenic animals.

3. Other Applications

Screening for P450RAI-2 Modulating Compounds

In another embodiment, the invention provides a method for identifying a compound or molecule that modulates P450RAI-2 protein activity or gene expression. “Modulate” as used herein can include activation or increase of P450RAI-2 protein activity or gene expression or suppression of P450RAI-2 protein activity or gene expression The method includes incubating components comprising the compound and P450RAI-2 peptide or a recombinant cell expressing P450RAI-2 peptide, under conditions sufficient to allow the components to interact and determining the effect of the compound on P450RAI-2 activity or expression. The effect of the compound on P450RAI-2 activity can be measured by a number of assays and may include measurements before and after incubation in the presence of the compound. Compounds that affect P450RAI-2 activity or gene expression include peptides, chemical compounds and biologic agents. Assays include Northern blot analysis of P450RAI-2 mRNA (for gene expression), Western blot analysis (for protein level) and luciferase, apoptosis or growth suppression assays (for protein activity).

The above screening assays may be used for detecting the compounds or molecules that bind to the P450RAI-2 protein or peptide, in isolating molecules that bind to the P450RAI-2 gene, for measuring the amount of P450RAI-2 in a sample, either peptide or RNA (mRNA), for identifying molecules that may act as agonists or antagonists, and the like.

Incubating includes conditions which allow contact between the test compound and P450RAI-2 peptide or with a recombinant cell expressing P450RAI-2 peptide. Contacting includes in solution and in solid phase, or in a cell. The test compound may optionally be a combinatorial library for screening a plurality of compounds. Compounds identified in the method of the invention can be further evaluated, detected, cloned, sequenced and the like, either in solution or after binding to a solid support by any method usually applied to the detection of a specific DNA sequence such as PCR, oligomer restriction, allele-specific oligonucleotide probe analysis, and the like.

Screening for P450RAI-2 or RA Related Disorders

Method for screening of P450RAI-2 protein activity and or gene expression as described above, can also be used to screen for P450RAI-2 related disorders. For instance, biological samples from patients with a particular conditions, such as cancer or APL, or other disorders outlined herein can be screened for P450RAI-2 protein activity and or gene expression. P450RAI-2 gene can also be sequenced from patients with a disorder to identify any mutations in the P450RAI-2 gene. Correlation between P450RAI-2 activity and/or gene expression/and or any mutations and the disorder can be determined by a number of methods known in the art. For instance, P450RAI-2 activity and/or gene expression of a subject to be screened can be compared with that from “healthy” individuals. In one embodiment, the level of P450RAI-2 activity and/or gene expression can be compared with a cut off level for normal P450RAI-2 activity and/or gene expression. In one embodiment, the cutoff level can be determined by analysis of a database of levels from “healthy” individuals.

Transgenic Animals and Methods of Making Same

Nucleic acids which encode proteins having biological activity of P450RAI-2 can be used to generate either transgenic animals or “knock out” animals which, in turn, are useful in the development and screening of therapeutically useful reagents. Preferably, non-human transgenic animals are encompassed within the scope of this invention. A transgenic animal (e.g., a mouse) is an animal having cells that contain a transgene, which transgene was introduced into the animal or an ancestor of the animal at a prenatal, e.g., an embryonic stage. A transgene is a DNA which is integrated into the genome of a cell from which a transgenic animal develops. In one embodiment, a P450RAI-2, preferably mouse or human cDNA shown in SEQ ID NO: 4, or an appropriate sequence, can be used to clone a murine P450RAI-2 gene in accordance with established techniques and the genomic nucleic acid used to generate transgenic animals that contain cells which express P450RAI-2 protein. Methods for generating transgenic animals, particularly animals such as mice, have become conventional in the art and are described, for example, in U.S. Pat. Nos. 4,736,866 and 4,870,009, 5,616,491. In a preferred embodiment, plasmids containing recombinant molecules of the invention are microinjected into mouse embryos. In particular, the plasmids are microinjected into the male pronuclei of fertilized one-cell mouse eggs; the injected eggs are transferred to pseudo-pregnant foster females; and, the eggs in the foster females are allowed to develop to term. [Hogan, B. et al., (1986) A Laboratory Manual, Cold Spring Harbor, N.Y., Cold Spring Harbor Laboratory]. Alternatively, an embryonal stem cell line can be transfected with an expression vector containing nucleic acid encoding a protein having P450RAI-2 activity and cells containing the nucleic acid can be used to form aggregation chimeras with embryos from a suitable recipient mouse strain. The chimeric embryos can then be implanted into a suitable pseudopregnant female mouse of the appropriate strain and the embryo brought to term. Progeny harbouring the transfected DNA in their germ cells can be used to breed uniformly transgenic mice.

Typically, particular cells would be targeted for P450RAI-2 transgene incorporation by use of tissue specific enhancers operatively linked to the P450RAI-2-encoding gene. For example, promoters and/or enhancers which direct expression of a gene to which they are operatively linked preferentially in cardiac muscle cells can be used to create a transgenic animal which expresses a P450RAI-2 protein. Examples of suitable promoters and enhancers include those which regulate the expression of the genes for cardiac myosin and cardiac actin. Transgenic animals that include a copy of a P450RAI-2 transgene introduced into the germ line of the animal at an embryonic stage can also be used to examine the effect of increased P450RAI-2 expression in various tissues.

The pattern and extent of expression of a recombinant molecule of the invention in a transgenic mouse is facilitated by fusing a reporter gene to the recombinant molecule such that both genes are co-transcribed to form a polycistronic mRNA. The reporter gene can be introduced into the recombinant molecule using conventional methods such as those described in Sambrook et al., 1989, Molecular Cloning, A Laboratory Manual. Cold Spring Harbor Laboratory press. Efficient expression of both cistrons of the polycistronic mRNA encoding the protein of the invention and the reporter protein can be achieved by inclusion of a known internal translational initiation sequence such as that present in poliovirus mRNA. The reporter gene should be under the control of the regulatory sequence of the recombinant molecule of the invention and the pattern and extent of expression of the gene encoding a protein of the invention can accordingly be determined by assaying for the phenotype of the reporter gene. Preferably the reporter gene codes for a phenotype not displayed by the host cell and the phenotype can be assayed quantitatively. Examples of suitable reporter genes include lacZ (b-galactosidase), neo (neomycin phosphotransferase), CAT (chloramphenicol acetyltransferase) dhfr (dihydrofolate reductase), aphIV (hygromycin phosphotransferase), lux (luciferase), uidA (b glucuronidase). Preferably, the reporter gene is lacZ which codes for b-galactosidase. b galactosidase can be assayed using the lactose analogue X-gal(5-bromo-4-chloro-3-indolyl b-D-galactopyranoside) which is broken down by b-galactosidase to a product that is blue in color. (See for example Old R. W. & Primrose S. B. Principles of Gene Manipulation. An Introduction to Genetic Engineering, 4th ed. Oxford University Press at pages 63-66 for a discussion of procedures for screening for recombinants).

Additionally, the non-human homologues of genes encoding proteins having P450RAI-2 activity can be used to construct a P450RAI-2 “knock out” animal which has a defective or altered P450RAI-2 gene. For example, a human P450RAI-2 cDNA, comprising the nucleotide sequence shown in SEQ ID NO: 5, or a mouse P450RAI-2 cDNA appropriate sequence thereof, can be used to clone a murine P450RAI-2 gene in accordance with established techniques. A portion of the genomic P450RAI-2 DNA (e.g., an exon) can be deleted or replaced with another gene, such as a gene encoding a selectable marker which can be used to monitor integration. The altered P450RAI-2 DNA can then be transfected into an embryonal stem cell line. The altered P450RAI-2 DNA will homologously recombine with the endogenous P450RAI-2 gene in certain cells and clones containing the altered gene can be selected. Cells containing the altered gene are injected into a blastocyst of an animal, such as a mouse, to form aggregation chimeras as described for transgenic animals. Chimeric embryos are implanted as described above. Transmission of the altered gene into the germline of a resultant animal can be confirmed using standard techniques and the animal can be used to breed animals having an altered P450RAI-2 gene in every cell. Accordingly, a knockout animal can be made which cannot express a functional P450RAI-2 protein. Such a knockout animal can be used, for example, to test the effectiveness of an agent in the absence of a P450RAI-2 protein.

Although experimental animals used in the preferred embodiment disclosed are mice, the invention should not be limited thereto. It can be desirable to use other species such as rats, hamsters and rabbits.

The transgenic animals of the invention can be used to investigate the effect of P450RAI-2 expression and activity or lack thereof and to test other compounds and molecules that can perhaps be used to suppress or restore the P450RAI-2 or RA activity. The transgenic animals of the invention can also be used to test substances for the ability to prevent, slow or reverse apoptosis. A transgenic animal can be treated with the substance in parallel with an untreated control transgenic animal.

Cells from the transgenic animals of the invention can be cultured using standard tissue culture techniques. In particular, cells carrying the recombinant molecule of the invention can be cultured and used to test substances for the ability to prevent, slow or reverse apoptosis.

EXAMPLES

General Materials and Methods

Cell Culture

HPK1a-ras (ras-transformed human keratinocyte), COS-1 (African green monkey kidney and V79 cells (Chinese Hamster lung) were maintained in DMEM supplemented with 10% FBS (5% for V79). WTE (human non-small cell lung carcinoma and SW900 (human non-small cell lung carcinoma) cells were maintained in RPMI supplemented with 10% FBS. SK-Luci-6 (human non-small cell lung carcinoma) and SK-MES-1 (human non-small cell lung carcinoma) cells in RPMI with 5% FBS. NB4(human acute prmyelocytic leukemia-serived) cells were maintained in RPMI supplemented with 10% FBS and gentamicin (10 mg/ml) HeLa cells (human cervical carcinoma) were maintained in MEM supplemented with 10% FBS. Previous cell lines were supplemented with penicillin (50 units/ml) streptomycin (50 ug/ml) and fungizone (0.1% final concentration). MCF-7 cells (human breast epithelial adenocarcinoma) were grown in MEM supplemented with 10% FBS, insulin (10 ng/ml), sodium pyruvate (0.5 mM), non-essential amino acids (100 nM), L-glutamine (2 mM), penicillin (5 ug.ml), streptomycin (5 ug/ml), fungizone (200 ng/ml), and gentamicin (10 mg/ml). All reagents were supplied by Life Technologies, NY. Cells lines were maintained at 37° C. in an atmosphere of 5% CO₂ and 95% air.

Transient Transfection of Cos-1 Celts

Exponentially growing cells were plated in triplicate into 6-well plates and transfected with lug of pcDNA3.1-P450RAI-1 or pcDNA3.1-P450RAI-2 using Fugene 6 transfection reagent with 3 ul per sample as described by the manufacturer (Roche Molecular Biochemicals, IN). Cells were maintained in media supplemented with 10% FBS during transfection.

RNA Preparation and Northern Blot Analysis

Total RNA was isolated from cultured cells uding the Oligotex Direct mRNA kit (Qiagen, CA) and electrophoresed on a formaldehyde-agarose gel. Gels were photographed under ultraiolet light and then blotted onto Hybond ECL nitrocellulose membrane (Amersham Pharmacia Biotech, UK) and fixed to the membrane by baking at 80° C. for 2 hours under vacuum. Prehybridization and hybridization steps were performed using ExpressHyb (Clontech, CA) according to the manufacturer's directions. Full length P450RAI-1 and P450RAI-2 cDNA were labeled with a-[³²P]dATP using Prime-A-Gene Labeling System (Promega, WI). The blot was washed two times for 15 minutes in 2×SSC, 0.1% SDS at room temperature then for 15 minutes at 60° C. in 0.1×SSC, and 0.1% SDS and exposed at −70° C. for 19 hours to Kodak X-Omat AR film (Eastman Kodak Company, NY).

Example 1 Determination cDNA Sequence Encoding P450RAI-2

The human expressed sequence tagged (EST) database at the National Center for Biotechnology Information (NCBI), available over the Internet at http://www.ncbi.nlm.nih.gov/BLAST/ was searched using an amino acid sequence encoding a typical heme binding motif found in all Cytochrome P450s. The database was queried using the following sequence: KKETFIPFGIGKRVCMGEQLAKMELFLMFV (SEQ ID NO1). The TBLASTN algorithm of the Advanced BLAST program was used to search all 6 possible reading frames for translation of all the human EST sequences against the query sequence (SEQ ID NO:1). Parameters for all searching were the defaults of Blosum 62 which use a gap existence cost of 11, per residue cost of 1 and lambda ratio of 0.85. Subject amino acid sequences which showed similarity to SEQ ID NO:1 were retrieved from the GenBank database and their nucleotide sequences used to search GenBank for nucleotide sequences showing similarity to the EST nucleotide query sequence using the BLASTN algorithm.

One of the subject sequences obtained from GenBank (AA012833, identified here as SEQ ID NO:2, a 3.5 kb clone from the Soares retina N2b4H2 library) showing similarity to the nucleotide sequence encoding amino acid sequence identified as SEQ ID NO:1, also showed similarity to a human genomic DNA sequence from GenBank (Accession#, AC007002 (clone name NH0493L16), identified here as SEQ ID NO: 3). As described below, the present inventors determined that this clone comprised within it the polynucleotide sequence encoding the novel cytochrome P450 of the invention, P450RAI-2. A BLASTN search of the EST database using SEQ ID NO:2 failed to identify any more EST sequences showing similarity. In order to check for protein sequences which may show similarity to the 6 possible reading frames for translation of SEQ ID NO:2, the BLASTX program was run on the non-redundant GenBank database. Several sequences with the highest degrees of amino acid similarity were identified and included, human, mouse, Xenopus and zebrafish P450RAI (CYP26A; protein encoded by SEQ ID NO:13 (human), protein encoded by SEQ ID NO:14 (zebrafish)).

Using the amino acid sequence of human P450RAI (SEQ ID NO:4 of WO 97/49815) aligned to the 3 possible reading frame translations of SEQ ID NO:3, a potential full-length amino acid sequence for a novel CYP cDNA family member was assembled. The intron/exon boundaries were deduced based on the loss of amino acid similarity. The intron/exon boundaries of the novel cytochrome P450 is shown in FIG. 1. The amino acids within the respective exons are identified above the schematic diagram and nucleotide positions in relation to human sequence are provided below the diagram. However, it would be appreciated that the positions of the exons noted in FIG. 1 are approximate and may vary slightly from the actual boundaries. The sequence has been termed P450RAI-2 based on its sequence homology with CYP26A. An amino acid sequence comparison between human P450RAI-2 and human p450RAI-1 is shown in FIG. 3. Overall the two protein sequences show 42% identity at the amino acid level and 52% at the nucleotide level over the region of the predicted open reading frame. The overall similarity of the two putative open reading frames is somewhat higher when conservatively substittued amino acids are considered.

Human retina Marathon-Ready cDNA (Clontech, California) was used as a template to amplify P450RAI-2 using the polymerase chain reaction (PCR) according to the manufacturer's directions Using the potential nucleotide sequence derived from the intron/exon mapping exercise, two primers, (SEQ ID NO:9 and SEQ ID NO:10) one upstream of the putative initial methionine and one downstream of the putative stop codon, were synthesized and used to PCR amplify a fragment of approximately 1600 base pairs representing the coding region SEQ. ID NO: 4 See FIG. 2 [SEQ ID NO:28] which depicts the original clone within the 1598 bp coding sequence and the 3 untranslated region which was cloned and sequenced. The 1598 bp fragment including the coding sequence of the cDNA is indicated as SEQ ID NO:4 and appears to correspond to a full-length cDNA. SEQ ID:4 shows a single nucleotide change from “C” in the genomic sequence SEQ ID NO:3 to “T” at nucleotide 1401 of SEQ ID NO:4 which, due to the degeneracy of the genetic code, does not change the corresponding amino acid sequence, identified as SEQ ID NO:5.

The cDNA 1600 bp PCR amplified product was gel purified using the QIAEXII Gel Extraction kit (Qiagen, California) and ligated into the pT-Adv vector using T4 DNA Ligase, heat shocked into competent TOP10F′ Escherichia coli, plated on Luria Bertoni-kanamycin plates and incubated overnight at 37° C., as per the manufactures instruction for the AdvanTAge PCR Cloning Kit (Clontech, CA). White colonies were grown up in Luria Bertoni-kanamycin medium, and DNA was prepared using the QIAprep Spin Miniprep kit (Quiagen, CA). For transient expression studies the P450RAI-2 cDNA was subcloned into the EcoR1 restriction endonucleoase site of pcDNA3.1 (Invitrogen, CA).

Example 2 P450RAI-2 Tissue Expression

Given the presence of a full-length cDNA in a retinal cDNA library, expression in human retinal tissues could be expected. In order to find tissues in which P450RAI-2 is expressed, a multi-tissue RNA dot blot containing samples from 76 different normal human tissues a human poly A+ blot (Clontech, CA) was probed using a labeled probe encoding the full length P450RAI-2 α-[³²P]dATP-labeled probe for the corresponding cDNAs were hybridized to blots using the conditions as described in the manufacturers directions. A human brain multi-tissue northern blot (Clontech, CA) was also hybridized with full-length α-[³²P]dATP-labelled P450RAI-2 probe according to the manufacurer's directions. The blots were stripped and re-probed with α-[³²P]dATP-labelled ubiquitin and β-actin controls.

FIG. 4 illustrates the results. P450RAI-2 appears to be expressed in a variety of tissues in differing levels (other data not shown) and at higher levels in tissues including kidney, lung, liver, spleen, fetal spleen, skeletal muscle, thymus, peripheral blood leukocyte, lymph node, bone, stomach, placenta, duodenum and pituitary gland. However, samples from human brain including pons (FIG. 4A, sample h1) and left and right cerebellum (FIG. 4A, samples a2 and b2 respectively) clearly show the highest levels of expression. FIG. 4C depicts the tissue map of the 76 tissue samples. In comparison, a similar blot probed with P450RAI-1 shows low level expression in most of the tissues with the absence of a distinct signal in any of the corresponding tissues from human brain (data not shown). Blots shown in FIGS. 4A and 4B are representative of multiple hybridization experiments. Two independent blots were utilized and each blot was hybridized with probes for P450RAI-2, P450RAI-1 and ubiquitin control (FIG. 4B in order to verify the results.

A human Northern blot (FIG. 4D)(Clontech, CA) comprising mRNAs from various brain tissues was also probed with P450RAI-2 [SEQ ID NO:4] according to the manufacturers directions. A hybridizing transcript of greater than 4.4 Kb was seen and is consistent with the size predicted by the cDNA clone isolated from human retina and from the predicted exons of the genomic clone that was identified. Consistent with the dot blot analyses, considerably higher levels of expression of transcripts for P450 RAI-2 are seen in the cerebellum. Lower but detectable levels of expression are observed in cerebral cortex, medulla, occipital pole, frontal lobe and temporal lobe. Other data from a Northern blot comprising mRNAs from multiple tissues indicated various levels of expression of P450RAI-2 in brain, heart, skeletal muscle, spleen, kidney, liver and small intestine. [Data not shown]

Example 3 Inducibility of P450RAI-2

The regulation of P450RAI-2 expression by various retinoids was checked in three different human cell lines, SKMES, CALU-1 and MCF-7. See FIGS. 5A (P450RAI-2 probe), B (blot was stipped and re-probed with β-actin) and C is ethidium bromide stained gel showing 18S and 28S RNAs. Tissue culture cells were incubated with each retinoid for 12 hours, total RNA prepared and a northern blot performed. The blot was hybridized with SEQ ID NO:4 using ExpressHyb (Clontech, CA) according to the manufacturer's directions at 65° C. The blot was washed as follows: 2×SSPE & 0.1% SDS two washes of 5 minutes each; 1×SSPE & 0.1% SDS one wash of 15 minutes at 65° C.; 0.1×SSPE & 0.1×SDS one wash of 15 minutes at 65° C. The blot was exposed to film for 66 hours. P450RAI-2 was found to be induced in MCF-7 cells in response to both all-trans retinoic acid and 13-cis retinoic acid. Whether or not 9-cis retinoic acid induces expression of P450RAI-2 is not clear from these results. It is known that aliquots of both 9-cis and 13-cis retinoic acid are frequently contaminated with all-trans retinoic acid.

P450RAI-2 expression was found to be inducible in the human keratinocyte cell line HPKIA-RAS. Cells in culture were incubated with all-trans retinoic acid at a final concentration of 10⁻⁶ M for 12 hours. Total RNA was prepared and a northern blot performed. The blot was hybridized at 65° C. using PerfectHyb (Sigma, MO) according to the manufacturer's directions. The blot was washed as follows: 2×SSC & 0.1% SDS two washes of 5 minutes each at room temperature; 1×SSC & 0.1% SDS one wash of 15 minutes at 65° C.; 0.1×SSC & 0.1% SDS three washes of 15 minutes each at 65° C. The blot was exposed to X-ray film overnight. The results are shown in FIG. 6.

The potential induction of mRNAs for P450RAI-2 in response to all-trans-RA was also evaluated.

Tissue culture cells were incubated with 1 μM all-trans-RA dissolved in dimethylsufoxide (DMSO) or DMSO alone for 12 hours, total RNA prepared and a northern blot analysis performed. The blot was hybridized at 65° C. using ExpressHyb (Clontech, CA) according to the manufacturers directions. The blot was washed as follows: 2×SSPE & 0.1% SDS two washes of 5 minutes each; 1×SSPE & 0.1% SDS one wash of 15 minutes at 65° C.; 0.1×SSPE & 0.1×SDS one wash of 15 minutes at 65° C. The blot was exposed to X-ray file for 66 hours.

RT-PCR was performed using 1 μg total RNA and the Advantage One-Step RT-PCR kit (Clontech, CA). The final primer concentrations were 45 μM for the P450RAI-2 primers and 11.25 μM for the GAPDH-specific primers. The thermal cycling program for cDNA synthesis and PCR amplification was 1 cycle at 50° C. for 1 hr, 1 cycle at 94° C. for 5 min, followed by 30 cycles of 94° C. for 30 sec, 65° C. for 30 sec, 68° C. for 1 min, and a final cycle for 68° C. for 2 min. The P450RAI-2 upstream amplification primer was 5′-TCCCTGCCTGTCGACCTGCCCTTC-3′ (SEQ ID NO: 29) and the downstream primer was 5′-GACACTCCAGCCTTTGGGGATCTG-3′ (SEQ ID NO: 30). The upstream and downstream primers to detect human glyceraldehyde-3-phsophate dehydrogenase mRNA were respectively, 5′-TGAAGGTCGGAGTCAACGGATTTGGT-3′ (SEQ ID NO:31) and 5′-CATGTGGGCCATGAGGTCCACCAC-3′ (SEQ ID NO:32).

The RT-PCR products were electrophoresed on a 1.2% agarose gel and blotted onto Hybond-N⁺ membrane (Amersham Pharmacia Biotech, UK). Hybridization was performed at 42° C. using ExpressHyb hybridization buffer (Clontech Laboratories Inc., CA) and probed with an interal P450RAI-2-specific oligonucleotide, 5′-GTGTGCCCTCGCAGGGGCAGCCGCCACTGTGC-3′ (SEQ ID NO: 33) that had been end-labeled using γ[³²P]ATP and T4 polynucleotide kinase. The membrane was subsequently stripped and re-probed with an internal-end labeled P450RAI-1-specific oligonucleotide, 5′-CGCCTCGGATGCCCGCAGCCC-GCAGATCTTGG-3′ (SEQ ID NO: 34) The membrane was again stripped and re-probed with an internal GAPDH oligonucleotide. The final wash for all hydbridizations was 0.1×SSC/0.1%, 50° C., 15 min, blots were exposed to Kodak X-0mat AR film (Eastman Kodak Co., NY).

Several human cell lines in culture were tested for expression and induction of expression of P450RAI-2 by treating cells with 1 μM all-trans-RA or DMSO for 12 hours followed by Northern blot and RT-PCR anaylses (FIG. 7A). Of the four cell lines tested by Northern analysis, three (HPKla-ras, HeLa and MCF-7) show induction of P450RAI-2 transcripts in response to all-trans-RA with MCF-7 showing the strongest induction.

Reverse transcription polymerase chain reaction (RT-PCR) analyses of transcripts from both control and all-trans-RA treated cultured cells demonstrate several important findings. As with P450RAI-1, P450RAI-2 shows multiple distinct modes of regulation of expression (FIG. 7B). NB4, V79, and SK-Luci-6 cells appear to have little or no perceptible transcripts for P450RAI-2 in either vehicle or all-trans-RA treated cells. Several cell lines, including MCF-7, HeLa, HPK1a-ras and WT-E show evidence for inducible expression of P450RAI-2 when cells are exposed to 1 μM all-trans-RA. Interestingly, SKMES-1 and SW900, shows constitutive expression of P450RAI-2 in both treated and untreated samples.

Using RT-PCR we also evaluated a brief time course of induction of PCR products corresponding to mRNA transcripts for P450RAI-2 in HPK1a-ras cells. These results (FIG. 7C) indicate that, at least in one cell line, transcripts for P450RAI-2 can be induced by all-trans-RA within 2 hours post-addition of inducer suggesting a direct transcriptional mechanism of induced.

Example 4 P450RAI-2 Homologs

The existence of homologs of P450RAI-2 in other species was explored. SEQ ID NO:4 and the BLASTN algorithm was used in a search of the NCBI EST database. Initially, three homologs were identified, one each from mouse, rat and zebrafish. The nucleotide sequences of these clones, SEQ ID NO:6, (mouse) SEQ ID NO:7 (rat) and SEQ ID NO:8 (zebrafish) show extensive similarity to SEQ ID NO:5. The corresponding amino acid sequences of the mouse and zebrafish are given as SEQ ID NOs:11 and 12, respectively.

The clones for mouse, zebrafish and rat are all partial cDNAs and encoding portions corresponding to portions of the full-length coding sequence of the human cDNA (SEQ ID NO:4). The zebrafish amino acid sequence, which shows homology to P450RAI-2, contains 167 amino acid residues. Of the 167 amino acids, 115 are identical to the human CYP26A sequence (i.e., when the amino acids are aligned using the Omiga software program (Oxford Molecular, Campbell, Calif.), version 1.13, with the default parameter settings for protein alignments, 115 are the same), giving a homology of about 68 percent. The rat sequence shows nucleotide homology to the 3′-untranslated region of human P450RAI-2 so no conclusion about the degree of homology to the coding region of P450RAI-2 can be made. The mouse amino acid sequence shows an absolute conservation with the human counterpart. Over a stretch of 92 amino acids beginning with the potential start methionine of the human P450RAI-2, all 92 amino acids are conserved between the mouse and human. At the nucleotide level there is 93.1 percent homology between the mouse and human. This degree of homology is exceptionally high, but this is a preliminary result in the sense that the full-length mouse sequences have yet to be obtained. The open reading frame of the mouse nucleotide sequence extends at least 111 amino acids upstream of the putative initial methionine in human P450RAI-2, raising a possible question as to the true origin of the mouse sequence.

Further searching of the NCBI Mouse EST database available over the internet at http://www.ncbi.nlm.nih.gov/blast/blast.cgi?[form=1] using the human P450RAI-2 sequence revealed three mouse EST clones, AW488377.1 (SEQ ID NO:18) which corresponds to human cDNA nucleotides 271-831, AW047279.1 (SEQ. ID. NO:19) which corresponds to human cDNA nucleotides 1-276 and includes 5′ UTR ATG is underlined in bold, wherein the sequence should be read backwards in antisense from this point, and EST BE864840.1 (SEQ. ID. NO:20) which corresponds to human cDNA nucleotides 1-118 and includes 5′UTR; ATG is marked. In sequencing clone AW488377, the inventors identified a novel sequence included therein, SEQ ID NO: 26. A further rat EST, SEQ ID NO: 27 was also identified that corresponds to human P450RAI-2 nucleotides 1-388.

The ESTs were used to search the HTGS database http://www.ncbi.nl m.nih.gov/blast/blast.cgi.?[form=1] wherein genomic mouse clone AC022779.3 was identified, potentially comprising the complete mouse nucleotide coding sequence of P450RAI-2. Using techniques similar to that used to identify the intro/exon boundaries of human P450RAI-2, the mouse clone was aligned with the human P450RAI-2 cDNA to detect similarities. Five of Six putative mouse exon sequences were identified: SEQ ID NO: 21 (corresponds to exon 1, mouse sequence 185832-186036), SEQ ID NO: 22 (corresponds to exon2, mouse sequence 189360-186590), SEQ ID NO: 23 (corresponds to exon 3, mouse sequence 196630-196905, SEQ ID NO: 24 (corresponds to exon 4, mouse sequence 197146-197303), and SEQ ID NO: 25 (corresponds to exon 6, mouse sequence 90745-90366).

Example 5 Metabolism of All-Trans Retinoic Acid by P450RAI-2

Analysis of All-Trans-RA Metabolism by HPLC.

48 hours post-transfection, cells were washed twice with DMEM medium (without serum) and then incubated in 0.5 ml DMEM medium containing 10% FBS and either 100 nM radiolabelled all-trans-RA (0.1 μCi/ml[³H]-RA; 5nCi/nmol) or unlabelled 1 μM all-trans-RA. After incubation for 3 hours at 37° C., in a light protected environment, total lipids were extracted as described previously by Bligh and Dyer [1957] as modified in White and Petkovich [1996b]. The aqueous soluble retinoid metabolites were quantified using β-scintillation counting. The organic soluble metabolites were dried under nitrogen gas, resuspended in 100 μl acetonitrile:water:acetic acid in the ratio 50:50:0.5 and analyzed by HPLC. HLPC was performed using a reverse phase column (150×4.6 mm C18 Zorbax-SB, Hewlett Packard) at a flow rate of 1 ml/min. The Mobile phase contained 10 mM ammonium acetate and consisted of an isocratic elution for 2 min with solvent A (acetonitrile; water: acetic acid 50:50:0.5) followed by a linear gradient over 18 min from solvent A to solvent B (acetonitrile: water: acetic acid 90:10:0.04) and then an isocratic elution with solvent B for an addition 5 min. Effluent from the HPLC column flowed directly to a radioflow detector LB (EG&G Berthold). The retinoids were detected at a wavelength of 351 nm and the ultraviolet spectrum of each metabolite peak was determined using photodiode array detection. Radioactivity as well as ultraviolet spectrum data was analyzed using Millenium 32 software (Waters, Mass.). Aqueous soluble radioactivity (FIGS. 14A and B) was calculated by integration of selected regions of the chromatograms. Three regions of the chromatograms were defined which represent: (I) the substrate peak (all-trans-RA); (ii) peaks with retention times between 8 and 12 minutes (4-OH region); and more polar peaks with retention times between 2 and 6 minutes (polar region).

Example 5A

Retinoic acid as a substrate of P450RAI-2 was studied. The full-length human P450RAI-2 cDNA was cloned into the eukaryotic expression vector pcDNA 3.1 (Invitrogen, CA). Exponentially growing COS-1 cells were plated in triplicate into 6 well plates and transiently transfected with 1 ug of pcDNA 3.1, pcDNA3.1-P450RAI-1, or pcDNA3.1-P450RAI-2 using Fugene 6 transfection reagent with 3 ul per sample as described by the manufacturer (Roche Molecular Biochemicals, IN) and then incubated with nanomolar concentrations of [11,12⁻³H]all-trans retinoic acid or micromolar concentrations of non-radioactive all-trans retinoic acid. COS-1 cells are an African green monkey kidney “fibroblast-like” cell line. The cell line was maintained in DMEM supplemented with 10% FBS at 37° C. in an atmosphere of 5% CO₂ and 95% air.

P450RAI-2 expression in COS-1 cells promoted the rapid conversion of RA into both lipid- and aqueous-soluble metabolites. See FIGS. 8 to 13. Fractions of total lipid extracts of transfected cells were initially separated by reverse-phase HPLC on Zorbax-SB C18 column (Hewlett Packard). HPLC conditions used a linear gradient of 50% acetonitrile, 49.9% H₂O, 0.1% acetic acid to 90% acetonitrile, 9.9% H₂O, 0.1% acetic acid with a flow rate of 1 ml/minute. Radioactivity was detected using a Berthold RadioFlow monitor. Using these conditions standard retinoids eluted at the following times: all-trans retinoic acid—20.5 minutes; 4-OH-retinoic acid—8.1 minutes; 4-oxo-retinoic acid—9.6 minutes; and 18-OH-retinoic acid—9.9 minutes. Comparison between extracts from pcDNA 3.1 and pcDNA 3.1-P450RAI-2 cells indicated that P450RAI-2 significantly increased all-trans retinoic acid metabolism. Incubation of P450RAI-2 transfected cells with micromolar concentrations of all-trans retinoic acid resulted in the production of multiple more polar peaks, some of which co-eluted with the standard retinoids. FIG. 8A shows an increase in aqueous-soluble radioactivity in P450RAI-2 transfected cells compared to media or pcDNA alone. FIG. 8B shows that there was an increase in lipid-soluble metabolites of all-trans retinoic acid when P450RAI-2 was transfected into the COS-1 cells. Metabolism of micromolar concentrations of non-radioactive all-trans retinoic acid was also evaluated. Transfected cells and controls were exposed to 1 micromolar all-trans retinoic acid for 3 to 4 hours and then analyzed for metabolism. Photo-diode array detection of HPLC-separated peaks are shown in FIGS. 10 to 13. FIG. 10 shows a background profile of media alone. FIG. 12 shows COS-1 cells transfected with the pcDNA plasmid alone. FIG. 12 shows the generation of more polar products when P450RAI (human) is transfected. In comparison, in FIG. 13, P450RAI-2 also causes the rapid metabolism of all-trans retinoic acid substrate to polar metabolites, several of which have the same retention times as the retinoid standards for 4-OH-retinoic acid and 4-oxo-retinoic acid. Although similar, there appear to be some differences in the ratios of individual metabolites in the profiles generated by P450RAI-2 compared to P450RAI.

Example 5B

COS-1 cells were transfected with either plasmid (pcDNA3.1-P450RAI-2 or pcDNA3.1-P450RAI-1). The cells were then incubated with, all-trans-RA substrate over a 3 hour incubation period. The all-trans-RA substrate was extensively metabolized to more polar aqueous soluble products (FIGS. 14 and 15). HPLC analysis using photodiode array detection was performed on samples prepared from transfected cells trated with 1 μM unlabelled all-trans-RA. FIGS. 14A, B and C show comparative chromatograms of the lipid-soluble extracts from pcDNA3.1-P450RAI-2 (FIG. 14A), pcDNA3.1-P450RAI-1 (FIG. 14B) and pcDNA3.1 transfected cells (FIG. 14C). In both pDNA3.1-P450RAI-2 and pcDNA3.1-P450RAI-1 transfected cells the generation of multiple more polar peaks is observed. There is also a significant decrease in all-trans-RA substrate when compared to pcDNA3.1 controls (compare RA peaks in FIGS. 14A, B, with C). Peaks labelled as 4-OH-retinoic acid, 4-oxo retinoic acid and 18-OH-retinoic and co-elute with standards of and show characteristics UV spectra of these metabolites. Additionally, multiple unidentified peaks (labeled 1-4; FIG. 14A) which show maxima characteristic of retinoids (data not shown) are generated and appear to be qualitatively similar in both P450RAI-2 and P450RAI-1 samples compared to controls.

To evaluate the efficiency of P450RAI-2 at more physiological concentration of substrate, P450RAI-1 transfected cells were exposed to 100 mM radiolablled (spec. act.) all-trans-retinoic acid (FIGS. 15A and B). In these cells, 34±0.2% of the all-trans-RA substrate is converted to aqueous-soluble products compared to 26±1.5% in the P450RAI-1 transfected cells (FIG. 15A). Controls, including media alone or pcDNA3.1 tranfected cells, show 1.6±0.1% (media alone) and 2.7±0.2% (pcDNA3.1) conversion of substrate to aqueous radioactivity.

The radioactivity remaining in the organic soluble fraction in the transfected cells exposed to 100 nM [³H] all-trans-retinoic acid (FIG. 15B) was also evaluated. HPLC analysis identified many more polar metabolites in both the P450RAI-2 and P450RAI-1 transfected cells compared to controls (data not shown). In media from cells transfected with pcDNA3.1-P450RAI-2 or pcDNA3.1-P450RAI-1 a high degree of disappearance of substrate compared to controls was observed. As well, there is a concomitant increase in the more polar lipid-soluable retinoid metabolites which elute in both the 4-OH and polar regions of the chromatograms. These results clearly indicate that expression of either P450RAI-2 or P450RAI-1 causes substantial metabolism of all-trans-RA to more polar metabolites (FIG. 15B).

Example 6 Retinoid Substrate Specificity of P450RAI-2

Given the presence of two unique enzymes P450RAI-1 and P450RAI-2, with the capacity to rapidly metabolize all-trans-RA the specificity of these two enzymes were evaluated. Interestingly, both P450RAI-1 and P450RAI-2 show approximately equal efficiencies at metabolizing all-trans-RA (FIGS. 15 and 16). Competition assays were also performed to evaluate the ability of five retinoids, all-trans-RA, 9-cis-RA, 13-cis-RA, retinal and retinol to compete out P450RAI-2 or P450RAI-1 mediated all-trans-RA metabolism (FIG. 16). The non-specific cytochrome P450 inhibitor, ketoconazole, was also tested.

COS-1 cells were transfected with either pcDNA3.1-P450RAI-1 or pcDNA3.1-P450RAI-2 in 6-well tissue culture plates as described above. 48 hours post-transfection cells were harvested, pooled, washed with DMEM medium and replated into duplicate 48-well plates with 5×10⁵ cells per well. The cells were incubated in 0.2 ml DMEM medium containing 0.05 μCi/ml [³H]-RA (final concentration 2 nM) in the present or absence of increasing concentrations of the each unlabelled retinoids (all-trans-RA, 9-cis-RA, 13-cis-RA, retinol, retinal). Control cells were incubated with increasing concentration of ketoconazole. After incubation for 3 hours at 37° C., the retinoids were extracted using the Bligh and Dyer [1957] procedure and the aqueous soluable RA-metabolites were counted in a scintillation counter as described above.

These compeition studies indicated that P450RAI-1 and, -2 exhibit comparable substrate specificies with all-trans-RA being the preferred substrate for both enzymes having ID₅₀ values of approximately 3.0 μM for P450RAI-2 and 2.5 μM for P450RAI-1. The other retinoids show varying abilities to compete out metabolism of all-trans-RA by P450RAI-2 and P450RAI-1 in the following rank order: 9-cis-RA>13-cis-RA>retinal≧retinol (see Table 1 for interpolated ID₅₀ values). Using microsomes prepared from stably-transfected P450RAI-1 cells we have also found the same relative levels of competition suggesting that the differences in ID₅₀ values are not due differences in cellular uptake of the retinoids (data not shown). TABLE 1 INTERPOLATED ID₅₀ VALUES P450RAI-1 P450RAI-2 All-trans-RA 2.5 3 9-cis-RA 32 25 13-cis-RA >75 55 Retinol >100 >100 Retinol >100 >100 Ketoconzole 16 12

Example 7 Expression of P450RAI-1 and P450RAI-2 in Human Cells

Total RNA aliquots (10 μg) were electrophoresed on a 1.0% formaldehyde-agarose gel and a northern blot performed. The gel was photographed under ultraviolet light and then blotted on Hybond ECL nitrocellulose membrane (Amersham Pharmacia Biotech, UK) and fixed to the membrane by baking at 80° C. for 2 hours under vacuum. Prehybridization and hybridization steps were performed using ExpressHyb (Clontech, CA) according to the manufacturer's directions. Three individual cDNA fragments were labeled with α-[³²P]dATP using the Prime-A-Gene Labeling System (Promega, WI). The probes were as follows; P450RAI-1762-1217 bp of SEQ ID NO:13, full length P450RAI-2 SEQ ID NO:4 and a human glyceraldehyde-3-phosphate dehydrogenase (GAPDH) PCR fragment. The blot was hybidized with P450RAI-2, washed two times for 5 minutes in 2×SSPE, 0.1% SDS at room temperature, then washed once at 65° C. for 10 minutes in 1×SSPE, 0.1% SDS and a final wash for 15 minutes at 65° C. in 0.1×SSPE, 0.1% SDS. The blot was exposed at −70° C. for 48 hours to Kodak X-Omat AR film (Eastman Kodak Company, NY). FIG. 17A shows P450RAI-2 expression was induced in the RAFT sample treated with Tazarotene. P450RAI-2 appears to also be expressed in the Day14 Psoriasis Biopsy sample treated with Tazarotene. The blot was stripped by washing two times for 30 minutes in boiling 0.5% SDS and exposed to film overnight to ensure proper removal of probe. The above protocol was repeated for P450RAI-1 and GAPDH. The P450RAI-1 and GAPDH blots were exposed for 96 and 4 hours respectively. Two separate hybridizations with a P450RAI-1 probe did not produce any bands on the northern blot.

RT-PCR was performed using lug of total RNA and the Advantage One-Step RT-PCR kit (Clontech, CA). The final primer concentrations were 45 μM for the P450RAI-1 and P450RAI-2 primers and 11.25 μM for the GAPDH-specific primers. Two separate sets of reactions were performed using the primer sets, P450RAI-1/GAPDH and P450RAI-2/GAPDH. The thermal cycling program for cDNA synthesis and PCR amplification was 1 cycle at 50° C. for 1 hour, 1 cycle at 94° C. for 5 minutes, followed by 30 cycles of 94° C. for 30 seconds, 65° C. for 30 seconds, 68° C. for 1 minute and a final cycle of 68° C. for 2 minutes. The P450RAI-1, P450RAI-2 and GAPDH upstream and downstream amplification primers sets were 5′GCCTTCGAGGAAATGACCCG-3′ (SEQ ID NO: 35) and 5′-CTGGATGCATCCTCTGGGTG-3′ (SEQ ID NO: 36), 5′-GTCTACCAGCAGTTTGTGGAC-3′ (SEQ ID NO: 37) and 5′-AGTCCAGGTAGCGCAGCCCACT-3′ (SEQ ID NO: 38), 5′-TGAAGGTCGGAGTCAACGGATTTGGT-3′ (SEQ ID NO: 39) and 5′-CATGTGGGCCATGAGGTCCACCAC-3′ (SEQ ID NO: 40) respectively. Total RNA isolated from MCF-7 cells treated with all-trans-RA was used as a positive control. FIG. 17B also shows expression of P450RAI-2 in the Tazarotene treated RAFT sample. Both the Psoriasis samples show PCR products corresponding to P450RAI-2.

Example 8 Expression of P450RAI-2 in Mouse Embryos

Probe synthesis: All in situ hybridization experiments were performed using an antisense copy of mouse EST AW488377.1 [SEQ ID NO:18] labelled with digoxigenin. The EST was cloned into pT7T3D, linearized with HindIII, and transcription was initiated from the T7 promoter. RNA labeling reactions were performed using DIG RNA labeling mix (Roche) as per instructed by the kit insert.

In Situ Hybridization: Mice were sacrificed by cervical dislocation, and embryos were dissected in 1×PBS, before being left to fix overnight in 4% paraformaldehyde at 4° C. The next day, embryos were washed twice with PBT (1×PBS, 0.1% Tween-20) for 5 minutes at 4° C. Embryos were washed 5 minutes each with 25, 50, 75% methanol in PBT, then twice with 100% methanol and then stored at −20° C. To rehydrate embryos, they were taken through the previous methanol series in reverse and washed twice with PBT. Then embryos were treated with 10 μg/mL proteinase K in PBT for the following times: 8.5 dpc (days post coitum)-no treatment; 9.5 dpc-3 minutes; 10.5 dpc-4 minutes; 11.5 dpc-5 minutes. 3 washes of 2 mg/mL glycine in PBT were performed for 5 minutes each. Embryos were refixed in 0.2% glutaraldehyde/4% paraformaldehyde in PBT for 20 minutes, and then washed twice with PBT for 5 min. 1 mL of prehybridization solution (5×SSC, 1% SDS, 5 μg/mL Yeast tRNA, μg/mL heparin) was added, and embryos were incubated at 70° C. After 1 hour, prehybridization solution was replaced with 1 mL of fresh solution containing 1 μg digoxigenin-labeled probe and left to hybridize overnight at 70° C. The next day, embryos were washed twice with prehybridization solution for 30 minutes at 70° C. Embryos were washed for 20 minutes at 70° C. with a 1:1 mix of prehybridization solution and 1×MABT (DIG Wash and Block Buffer Set, Roche). After 3 rinses with MABT, embryos were washed twice for 30 minutes at 70° C. with MABT. To preblock embryos, 1×MABT/2% Blocking Reagent (DIG Wash and Block Buffer Set, Roche) was added. After an hour, solution was removed and replaced with 1×MABT/2% Blocking Reagent/20% sheep serum and left for 1 hour. Next, 1×MABT/2% Blocking Reagent/20% sheep serum/0.0005 Anti-Digoxigenin Antibody coupled to Alkaline Phosphatase (Roche) was added at left overnight at 4° C. The next day, embryos were rinsed 3 times with 1×MABT with 2 mM levamisole, and washed five times for 1 hour in 1×MABT/2 mM levamisole. Two washes of 10 minutes each were performed in NTMT (100 mM NaCl, 100 mM Tris-HCl, pH=9.5, 50 mM MgCl2, 2 mM levamisole). 1 mL of fresh NTMT was added along with 3.5 μL BCIP and 4.5 μL NBT (Gibco), and colour reaction was allowed to proceed in the dark. When complete, embryos were rinse twice with PBT, and refixed overnight at 4° C. in 0.2% glutaraldehyde/4% paraformaldehyde. The next day, embryos were washed for 1 hour in 1:1 CMFeT:glycerol before transfer to 4:1 CMFeT:glycerol until ready to photograph.

FIG. 18 illustrates P450RAI-2 in 8.0 and 8.5 dpc mouse embryos. (A) 8.0 dpc lateral view. No apparent staining. (B) 8.0 dpc, dorsal view. Staining at anterior end of neutral folds. (C) 8.5 dpc, lateral view. Expression is evident, possibly in presumptive rhombmeres 2, 5, and 6. (D) 8.5 dpc, dorsal view, rhombomere expression of RAI2 is clearly evident. TL: Tail; YS Yolk Sac; NF: Folds; pr: Presumptive Rhombomeres.

FIG. 19 illustrates P450RAI2 in 9.0 and 10.5 dpc mouse embyros. (A) 9.0 dpc, lateral view. Specific staining is visible in the eye, and rhombomeres 5 and 6. Diffuse staining is visible where the hind bud is beginning to form. (B) 9.0 dpc, dorsal view. Rhombomeres 5 and 6 show RAI2 expression. (C) 10.5 dpc, lateral view. The otic vesicle and eye are stained. (D) 10.5 dpc, dorsal view. Specific staining is observed in both otic vesicles as well as the hind limb bud. HL: hind limb bud; OV: Otic Vesicle.

FIG. 20 illustrates P450RAI2 staining in 11.5 dpc mouse embryo (A) 11.5 dpc, laterial view, staining is visible in both the fore and hindlimb bud. (B) 11.5 dpc, ventral view. Expression of P450RAI2 in both limb buds (C) Close up of forelimb bud, showing a lack of expression in the apical ectodermal ridge FL: Forelimb bud; HL: Hindlimb bud; AR: Apical Ectodermal Ridge.

FIG. 21 illustrates P450RAI-2 Staining in Embryos Treated with Retinoic Acid (A) 8.5 dpc, lateral view, staining is observed in rhombomere 5 and the tail mesoderm as indicated by the arrow. (B) 8.5 dpc, dorsal view clearly showing P450RAI2 expression in rhombomere 5. (C) 9.5 dpc, lateral view, expression of P450RAI2 is observed in rhombomeres 5 and 6, the developing hindlinb, somites and posterior mesoderm. (D) 9.5 dpc, dorsal view, expression is evidenct in rhombomeres 3,5 and 6 and in trunk ectoderm as indicated by the arrow. r: rhombomere; HL; Limb bud.

FIG. 22 illustrates P450RAI-2 expression in 11.5 dpc embryos treated with retinoic acid. (A) 11.5 dpc, lateral view, P450RAI2 expression is observed in both the developing hind and fore limb. (B) 11.5 dpc, ventral view, as in embryos untreated with retinoic acid, P450RAI2 expression is not observed in the aptical ectodermal ridge.

Example 9 Assays Using Cell Lines Expressing Different P450RAI's

P450RAI-1 and -2 expression plasmids can be used to generate transfected cells. Plasmid vectors such as pcDNA3.1 (Invitrogen, CA) are used to express cDNA of interest in the cells. Cells such as COS-1 or Hela could be used as the host for this purpose. Cells are then exposed to either low concentrations (picomolar) of a radioactive agent (substrate) or higher concentrations (micromolar) of non-radioactive agent (substrate) and the metabolic profile determined (see Example 5 and international patent publication No. WO 97/49815 in which all-trans retinoic acid is a substrate but other retinoid or retinoid type compounds can be used). The time of incubation of the cells can vary from 1 hour to 24 or 48 hours depending on the amount of agent and levels of expression of the protein of interest. The representative metabolite profiles are determined using phase extraction and HPLC. In the case of radioactive substrate B-scintillation counting can also be used if the metabolites produced segregate preferentially into one phase, as in the case of P450RAI-1 and RAI-2 when looking at all-trans retinoic acid metabolism. In comparative testing of potential modulators of P450RAI-1 or P405RAI-2, the modulators could be added to the cells at the same time as the substrate. Specificity of the modulator is determined by examining the degree to which its addition affects either the disappearance of substrate or the production of metabolites.

Example 10 Preparation of Antibodies

Monoclonal antibodies (Mab's) specific for P450RAI-2 are useful, for example, for diagnostic purposes such as for determining P450RAI-2 protein levels in the identification of normal and tumor tissues which metabolize RA. To produce these antibodies, purified P450RAI-2 protein is prepared. The human P450RAI-2 protein is produced in bacterial cells as a fusion protein with glutathione-5-transferase using the vector pGEX2 (Pharmacia). This permits purification of the fusion protein by GSH affinity chromatography. In another approach, P450RAI-2 is expressed as a fusion protein with the bacterial maltose binding domain. The fusion protein is thus recovered from bacterial extracts by passing the extract over an amylose resin column followed by elution of the fusion protein with maltose. For this fusion construct, the vector pMalC2, commercially available from New England Biolabs, is used. This vector has been used in the past, for example, to overexpress nuclear receptor proteins which were recovered in high yields for functional studies and the production of receptor specific antisera [Ohno, 1993]. The preparation of a second fusion protein is also useful in the preliminary screening of MAb's.

The generation of hybridomas expressing monoclonal antibodies recognizing P450RAI-2 protein is carried out as follows: BALB/c mice are injected intraperitoneally with protein/adjuvant three times at one-month intervals, followed by a final injection into the tail vein shortly prior to cell fusion. Spleen cells are harvested and fused with NS-1 myeloma cells (American Type Culture Collection, Rockville, Md.) using polyethylene glycol 4000 according to standard protocols [Kennett, 1979; Mirski, 1989]. The cell fusion process is carried out as described in more detail below.

The fused cells are plated into 96-well plates with peritoneal exudate cells and irradiated spleen cells from BALB/Ccmice as feeder layers and selection with hypoxanthine, aminopterin, and thymidine (HAT medium) is performed.

An ELISA assay is used as an initial screening procedure. 1-10 μg of purified P450RAI-2 (cleaved from the fusion protein) in PBS is used to coat individual wells, and 50-100 μl per well of hybridoma supernatants is incubated. Horseradish peroxidase-conjugated anti-mouse antibodies are used for the colorimetric assay.

As a secondary screening, cells which exhibit no detectable expression of P450RAI-2 message and no detectable RA metabolizing activity in the absence of retinoic acid, but in which P450RAI-2 exposure to RA induces expression of P450RAI-2, are used.

Positive hybridomas are cloned by limiting-dilution and grown to large-scale for freezing and antibody production. Various positive hybridomas are selected for usefulness in western blotting and immunohistochemistry, as well as for cross reactivity with P450RAI-2 proteins from different species.

The selected MAb's are useful for monitoring the levels of expression of P450RAI-2 protein following RA treatment in cell culture and in tissues. P450RAI-2 protein expression may be a prognostic indicator for determining whether a particular tumor will respond to RA treatment. There is also a wide intersubject variability in baseline RA metabolism and there is evidence suggesting that subjects with a high rate of RA metabolism have a higher incidence of squamous or large cell cancers of the lung [Rigas, 1996]. Once useful antibodies are characterized, these antibodies are used to survey tumor tissue samples for P450RAI-2 expression.

Protocol for Production of Mouse Hybridomas

Fusion

Feeder cells (spleen and peritoneal exudate cells) are plated. 24 to 48 hours before fusion, mouse myeloma cells are taken off drug (8-azaguanine 20 μg/ml) and counted to ensure that there are at least 50×10⁶ cells. 2 g of PEG 4000 are autoclaved in a glass tube for 15 minutes and maintained at 60° C. for use or alternatively stored at room temperature and remelted in a 60° C. water bath when needed.

BALB/c mice are immunized as per desired schedule. The final injection is given intravenously in the tail vein. Fusion of immunized spleen cells is carried out 3 or 4 days after the intravenous injection. Spleen from each animal is collected separately; eye sera for ELISA if desired.

A single cell suspension is prepared using a Teflon pestle and decanting connective tissue. The suspension is washed 1× in serum-free medium. Each spleen has about 10×10⁶ cells. The myeloma cells are collected, counted and washed in serum-free medium.

The cells are then fused. A small beaker of water, and serum-free medium (37° C.) are prepared and the PEG melted at 50-60° C. The immunized spleen cells and myeloma cells are mixed in a 50 ml TC tube (recommended ratios vary from 1:1 to 2:1) and the cells are washed once with serum-free medium. The supernatant is carefully discarded. 2.4 ml pre-warmed serum-free medium is added immediately with pipette to the melted PEG and mixed, maintaining the temperature at 37° C. in beaker of warm water. The PEG should be light pink. If it is yellow, another aliquot should be used. 0.5-1.0 ml of PEG is added dropwise to the cell pellet over 1 minute with gentle rotation of the tube or gentle stirring to ensure mixing. The tip of the addition pipette is placed directly over the cell pellet. The tube is swirled gently in 37° C. water bath for 90 seconds with the blunt end of a 3 ml pipette tip and 10 ml warm serum-free medium added slowly over 6-10 minutes while rotating tube gently to bring the volume up to 20-50 ml. The tube is maintained at 37° C. for at least 20 minutes to obtain cell fusion and then the cells are washed 2× with serum-free medium. The cells are centrifuged and gently resuspended in 100 ml of pre-warmed medium +10-20% FBS. 100 μl/well aliquotted in 96-well plates. Assuming one spleen fused with 100×10⁶ cells myeloma fusion partner, about 10 plates are needed. On the following day, 100 μl medium is removed and 100 μl 2×HAT added. Feed with 1×HAT medium for 1 to 3 weeks, then feed with HT medium (i.e., remove ½ HAT medium and replace with equal volume HT medium).

Preparation of Peritoneal Exudates and Spleen Feeder Cells

A sacrificed mouse is sprayed with 70% alcohol, skin is nicked and torn apart, with care being taken not to cut the peritoneum. The peritoneum is lifted with forceps and a needle is introduced; 5 ml of serum-free medium is slowly injected. The abdomen is massaged and the fluid is slowly sucked up, collected in a sterile tube and kept on ice. The volume is brought up to 5 ml. The spleen is obtained and placed in a sterile tube containing serum-free medium. The spleen is gently mashed with a sterile Teflon pestle. Clumps are allowed to settle and the cells are decanted into a clean tube, care being taken to avoid including connective tissue, in order to minimize fibroblast growth. The sample is irradiated at 4500 R. Cells are washed once with serum-free medium, placed into 96-well plates [one spleen/10 plates (approximately 2-5×10⁵ cells/well) and peritoneal exudate cell suspension (PECS) (<3×10³ cells/well) in a total volume of 100 μl/well] and incubated at 37° C. until ready to be used. They can also be stored in sterile tube overnight at 4° C.

Example 11 Screening Potential Modulators of P450RAI-2

Antisense nucleic acids or oligonucleotides (RNA or preferably DNA) that inhibit cellular RA-induced P450RAI-2 production can be used to inhibit metabolism of RA by P450RAI-2 [Monia, 1996]. Antisense oligonucleotides, typically 15 to 20 bases long, bind to the sense mRNA or pre mRNA region coding for the protein of interest, which can inhibit translation of the bound mRNA to protein. The cDNA sequence encoding human P450RAI-2 can thus be used to design a series of oligonucleotides which together span a large portion, or even the entire cDNA sequence. These oligonucleotides can be tested to determine which provides the greatest inhibitory effect on the expression of the protein [Stewart, 1996]. This can be done by exposing cells to the various oligonucleotides and measuring subsequent changes in human P450RAI-2 activity or by using antibodies to screen for inhibition of P450RAI-2 synthesis. The most suitable mRNA target sites include 5′- and 3′-untranslated regions as well as the initiation codon. Other regions might be found to be more or less effective. Alternatively, an antisense nucleic acid or oligonucleotide may bind to P450RAI-2 DNA coding or regulatory sequences.

Rather than reducing RA metabolism by inhibiting P450RAI-2 gene expression at the nucleic acid level, activity of the P450RAI-2 protein may be directly inhibited by binding to an agent, such as, for example, a suitable small molecule or a monoclonal antibody.

The present invention thus includes a method of screening drugs for their effect on activity (i.e., as a modulator, preferably an inhibitor) of a retinoic acid inducible protein. The method includes exposing the protein to a prospective inhibitor (or modulating) drug and determining the effect on protein activity. The measured activity might be hydroxylation of a retinoid, particularly all-trans retinoic acid, or hydroxylation of a retinoic acid, particularly all-trans retinoic acid, at the 4 position of the β-ionone ring thereof. For screening drugs for use in humans, P450RAI-2 itself is particularly useful for testing the effectiveness of such drugs. Prospective drugs could also be tested for inhibition of the activity of other P450 cytochromes, which are desired not to be inhibited. In this way, drugs which selectively inhibit P450RAI-2 over other P450s could be identified.

Another system for screening for potential modulators, preferably inhibitors, of a P450RAI-2 protein includes a stably transfected cell line having incorporated therein DNA of a reporter gene (e.g., β-galactosidase, firefly luciferase, or the like) and of the P450RAI-2, in which expression of both genes is inducible by exposure of the cells to RA. Expression of the reporter gene provides a measure of the induction of the expression system and therefore provides an indication of the amount of RA present. Exposure of the cells to RA leads to RA metabolism and, with time, such metabolism leads to a decrease in the degree of induction which is indicated by the reporter protein. Exposure of the cells to RA in the presence of an agent that inhibits P450RAI-2 metabolism of RA results in decreased RA metabolism, whereas exposure of the cells to RA in the presence of an agent that does not inhibit P450RAI-2 metabolism of RA has no effect on RA metabolism. A comparison of expression of the reporter gene in the presence of RA alone and in the presence of both RA and a potential inhibitory drug thus gives a measure of the effectiveness of the drug in inhibiting metabolism of RA by the P450RAI-2 protein.

One system for screening for potential inhibitors of a P450RAI-2 protein includes a cell line in which the endogenous P450RAI-2 gene is not present or not functional or not expressed. In this cell line, a cytochrome P450RAI-2 expression vector and an RA-inducible reporter gene are incorporated such that exposure of the cell line to RA results in metabolism of RA by the expressed P450RAI-2 protein and a degree of induction of the reporter gene based on remaining active RA. The addition of an inhibitor of P450RAI-2 will decrease the rate of metabolism/degradation of RA and therefore increase the activation/induction of the RA sensitive reporter gene.

Another system for screening of potential inhibitors (or other modulators) using the same cell line would be to add radioactive substrate to the cells along with the potential inhibitors (or modulators). Addition of the radioactive substrate, which could be all-trans retinoic acid, causes the production of radioactive metabolites. Using a phase extraction procedure, such as that described herein, the amount of these metabolites can be measured. The addition of an inhibitor will cause a decrease in the generation of the radioactive metabolites, which can be measured using β-scintillation counting or HPLC.

The invention thus provides a system for screening potential inhibitors of RA catabolism by a P450RAI-2 protein. The system includes a transfected cell line having incorporated therein DNA of a reporter gene, for example the luciferase gene exemplified above, in which expression of the reporter gene is inducible by exposure of the cells to RA. In this system, the P450RAI-2 gene is omitted, that is the reporter gene is under the control of the native promoter for the P450RAI-2 gene. Expression of the reporter gene provides a measure of the induction of the expression system and therefore provides an indication of the amount of mRNA produced in response to exposure of the cells to RA. Exposure of the cells to RA in the presence of an agent that inhibits induction of the expression system indicates that the agent is a potential inhibitor of RA catabolism, i.e., provides a measure of the effectiveness of the agent as a drug in inhibiting the expression of P450RAI-2 gene and thus metabolism of RA.

There is the possibility that cellular retinoic acid-binding protein (CRABP) [Adamson, 1993] is involved in binding of a retinoid substrate to a P450RAI-2 protein of the present invention. The effect of the presence of CRABP, derivatives, synthetic fragments or analogs thereof could thus be determined according to screening methods of the present invention; effectiveness of such agents in enhancing RA metabolism can also be determined.

The present invention allows the skilled artisan to prepare bispecific antibodies and tetrameric antibody complexes. Bispecific antibodies can be prepared by forming hybrid hybridomas [Staerz, 1986a &b].

The present invention includes three types of compounds related to retinoids: those that inhibit enzymatic activity of P450RAI-2, thereby inhibiting metabolism of RA; those retinoids that evade metabolism by P450RAI-2; and those compounds that repress induction of P450RAI-2 gene expression.

Compositions of the invention are administered to subjects in a biologically compatible form suitable for pharmaceutical administration in vivo. By “biologically compatible from suitable for administration in vivo” is meant a form of the composition to be administered in which any toxic effects are outweighed by the therapeutic effects of the composition. The term “subject” is intended to include living organisms in which a desired therapeutic response can be elicited, e.g. mammals. Examples of subjects include human, dogs, cats, mice, rats and transgenic species thereof. Administration of a therapeutically active amount of the therapeutic compositions of the present invention is defined as an amount effective, at dosages and for periods of time necessary to achieve the desired result. For example, a therapeutically active amount of a compound that inhibits catabolism of RA by a P450RAI-2 protein may vary according to factors such as the disease state, age, sex, and weight of the individual, as well as target tissue and mode of delivery. Dosage regimes may be adjusted to provide the optimum therapeutic response. For example, several divided doses may be administered daily or the dose may be proportionally reduced as indicated by the exigencies of the therapeutic situation.

Compounds of the present invention, such as those that are found to inhibit metabolism of RA by P450RAI-2 enzymes and that are useful as anticancer agents and in the treatment, amelioration, or prevention of skin disorders for which retinoic acid is useful, for example, may be used topically. In this regard they may be included in compositions for therapy in animals, including humans, for premalignant epithelial cell lesions, as a prophylaxis against tumor promotion in epithelial cells and treatment for dermatoses such as ichthyoses, follicular disorders, benign epithelial disorders, and other proliferative skin diseases, such as acne, psoriasis, eczema, atopic dermatitis, nonspecific dermatitis and the like.

Topical compositions are usually formulated with a pharmaceutically acceptable carrier in liquid, semi-solid or solid form. A pharmaceutically acceptable carrier is a material that is nontoxic and generally inert and does not affect the functionality of the active ingredients adversely. Such materials are well known and include those materials sometimes referred to as diluents or vehicles (excipients) in the pharmaceutical formulation art. The carrier may be organic or inorganic in nature. Examples of pharmaceutically acceptable carriers are water, gelatin, lactose, starch, mineral oil, cocoa butter, dextrose, sucrose, sorbitol, mannitol, gum, acacia, alginates, cellulose, talc, magnesium stearate, polyoxyethylene sorbitan monolaurate, and other commonly used pharmaceutical carriers. In addition to an active ingredient and carrier, the formulation may contain minor amounts of additives such as flavoring agents, coloring agents, thickening or gelling agents, emulsifiers, wetting agents, buffers, stabilizers, and preservatives such as antioxidants.

Certain compositions may be administered enterally. For oral administration, suitable forms are, for example, tablets, pills, syrups, suspensions, emulsions, solutions, powders and granules.

As anti-tumor agents or as part of an anti-tumor formulation, for example, compounds of the present invention can be used in a similar manner to retinoids used for treating various tumours, such as all-trans retinoic acid. The dose to be administered, whether a single dose, multiple does or daily dose, will of course vary with the particular compound employed because of the varying potency of the active ingredient, the chosen route of administration, the size of the recipient, the type of tumor, and the nature of the patient's condition. The dosage to be administered is not subject to definite bounds, but it will usually be an effective amount, or the equivalent on a molar basis of the pharmacologically active free form produced from a dosage formulation upon the metabolic release of the active drug to achieve its desired pharmacological and physiological effects. An oncologist skilled in the art of cancer treatment will be able to ascertain without undue experimentation, appropriate protocols for the effective administration of the compounds of this present invention.

Nucleic acids which encode proteins having biological activity of a P450RAI-2 protein can be used to generate either transgenic animals or “knock out” animals which, in turn, are useful in the development and screening of therapeutically useful reagents. A transgenic animal (e.g., a mouse) is an animal having cells that contain a transgene, which transgene was introduced into the animal or an ancestor of the animal at a prenatal, e.g., an embryonic stage. A transgene is a DNA which is integrated into the genome of a cell from which a transgenic animal develops. In one embodiment, a human P450RAI-2 cDNA, comprising the nucleotide sequence shown in SEQ ID NO:4, or an appropriate variant or subsequence thereof, can be used to generate transgenic animals that contain cells which express human P450RAI-2 protein. Methods for generating transgenic animals, particularly animals such as mice, have become conventional in the art are described, for example, in U.S. Pat. Nos. 4,736,866 and 4,870,009. In a preferred embodiment, plasmids containing recombinant molecules of the invention are microinjected into mouse embryos. In particular, the plasmids are microinjected into the male pronuclei of fertilized one-cell mouse eggs; the injected eggs are transferred to pseudo-pregnant foster females; and, the eggs in the foster females are allowed to develop to term. [Hogan, 1986]. Alternatively, an embryonal stem cell line can be transfected with an expression vector comprising nucleic acid encoding a protein having P450RAI-2 activity, and cells containing the nucleic acid can be used to form aggregation chimeras with embryos from a suitable recipient mouse strain. The chimeric embryos can then be implanted into a suitable pseudopregnant female mouse of the appropriate strain and the embryo brought to term. Progeny harboring the transfected DNA in their germ cells can be used to breed uniformly transgenic mice.

Typically, particular cells would be targeted for P450RAI-2 transgene incorporation by use of tissue specific enhancers operatively linked to the P450RAI-2 encoding gene. For example, promoters and/or enhancers which direct expression of a gene to which they are operatively linked preferentially in cardiac muscle cells can be used to create a transgenic animal which expresses a P450RAI-2 protein preferentially in cardiac muscle tissue. Examples of suitable promoters and enhancers include those which regulate the expression of the genes for cardiac myosin and cardiac actin. Transgenic animals that include a copy of an P450RAI-2 transgene introduced into the germ line of the animal at an embryonic stage can also be used to examine the effect of increased P450RAI-2 expression in various tissues.

The pattern and extent of expression of a recombinant molecule of the invention in a transgenic mouse is facilitated by fusing a reporter gene to the recombinant molecule such that both genes are co-transcribed to form a polycistronic mRNA. The reporter gene can be introduced into the recombinant molecule using conventional methods such as those described in Sambrook et al., [Sambrook,1989]. Efficient expression of both cistrons of the polycistronic mRNA encoding the protein of the invention and the reporter protein can be achieved by inclusion of a known internal translational initiation sequence such as that present in poliovirus mRNA. The reporter gene should be under the control of the regulatory sequence of the recombinant molecule of the invention and the pattern and extent of expression of the gene encoding a protein of the invention can accordingly be determined by assaying for the phenotype of the reporter gene. Preferably the reporter gene codes for a phenotype not displayed by the host cell and the phenotype can be assayed quantitatively. Examples of suitable reporter genes include lacZ ($-galactosidase), neo (neomycin phosphotransferase), CAT (chloramphenicol acetyltransferase) dhfr (dihydrofolate reductase), aphIV (hygromycin phosphotransferase), lux (luciferase), uidA ($-glucuronidase). Preferably, the reporter gene is lacZ which codes for $-galactosidase. $-galactosidase can be assayed using the lactose analogue X-gal (5-bromo-4-chloro-3-indolyl-b-D-galactopyranoside) which is broken down by $-galactosidase to a product that is blue in color [Old].

Although experimental animals used in the preferred embodiment disclosed are mice, the invention should not be limited thereto. It can be desirable to use other species such as, for example, rats, hamsters, rabbits and sheep.

The transgenic animals of the invention can be used to investigate the molecular basis of RA metabolism. The transgenic animals of the invention can also be used to test substances for the ability to prevent, slow or enhance RA metabolism. A transgenic animal can be treated with the substance in parallel with an untreated control transgenic animal.

Cells from the transgenic animals of the invention can be cultured using standard tissue culture techniques. In particular, cells carrying the recombinant molecule of the invention can be cultured and used to test substances for the ability to prevent, slow or enhance RA metabolism.

Additionally, the non-human homologs of genes encoding proteins having P450RAI-2 activity can be used to construct a “knock out” animal which has a defective or altered P450RAI-2 gene. For example, with established techniques, a portion of murine genomic P450RAI-2 DNA (e.g., an exon), can be deleted or replaced with another gene, such as a gene encoding a selectable marker which can be used to monitor integration. The altered P450RAI-2 DNA can then be transfected into an embryonal stem cell line. The altered P450RAI-2 DNA will homologously recombine with the endogenous P450RAI-2 gene in certain cells and clones containing the altered gene can be selected. Cells containing the altered gene are injected into a blastocyst of an animal, such as a mouse, to form aggregation chimeras as described for transgenic animals. Chimeric embryos are implanted as described above. Transmission of the altered gene into the germline of a resultant animal can be confirmed using standard techniques and the animal can be used to breed animals having an altered P450RAI-2 gene in every cell [Lemoine, 1996]. Accordingly, a knockout animal can be made which cannot express a functional P450RAI-2 protein. Such a knockout animal can be used, for example, to test the effectiveness of an agent in the absence of a P450RAI-2 protein.

The antisense nucleic acids and oligonucleotides of the invention are useful for inhibiting expression of nucleic acids (e.g. mRNAs) encoding proteins having P450RAI-2 activity. Since proteins having P450RAI-2 activity are associated with metabolism of agents which can act on the cell, e.g., RA, decreasing expression of such proteins can increase sensitivity of the cell to such agents. Antisense nucleic acids can be introduced into a drug resistant cell in culture to inhibit P450RAI-2 expression. One or more antisense nucleic acids, such as oligonucleotides, can be added to cells in culture media, typically, for example, at 200 μg/ml.

The antisense nucleic acids of the invention, or oligonucleotides thereof, can thus be used in gene therapy to correct or prevent retinoic acid or other retinoid resistance in a subject. For example, antisense sequences can be used to render retinoic acid or other retinoid resistant malignant cells sensitive to chemotherapeutic agents. Administration of antisense nucleic acids to a subject may be most effective when the antisense nucleic acid is contained in a recombinant expression vector which allows for continuous production of antisense RNA. Recombinant molecules comprising an antisense nucleic acid or oligonucleotide thereof, can be directly introduced into tissues, including lung tissue in vivo, using delivery vehicles such as liposomes, retroviral vectors, adenoviral vectors and DNA virus vectors. A delivery vehicle can be chosen which can be targeted to a cell of interest in the subject (e.g. a retinoid resistant tumor cell). Antisense nucleic acids can also be introduced into isolated cells, such as those of the haematopoietic system, ex vivo using viral vectors or physical techniques such as microinjection and electroporation or chemical methods such as coprecipitation and incorporation of DNA into liposomes, and such cells can be returned to the donor. Recombinant molecules can be delivered in the form of an aerosol or by lavage.

Accordingly, the invention provides a method for inhibiting retinoic acid or other retinoid resistance of a resistant cell by introducing into the resistant cell a nucleic acid which is antisense to a nucleic acid which encodes the protein identified as SEQ ID NO:5.

The nucleic acids of the invention can further be used to design ribozymes which are capable of cleaving a single-stranded nucleic acid encoding a protein having P450RAI-2 activity, such as an mRNA. A catalytic RNA (ribozyme) having ribonuclease activity can be designed which has specificity for a P450RAI-2-encoding mRNA based upon the sequence of a nucleic acid of the invention. For example, a derivative of a Tetrahymena L-191VS RNA can be constructed in which the base sequence of the active site is complementary to the base sequence to be cleaved in a P450RAI-2-encoding mRNA. [Cech a and b]. Alternatively, a nucleic acid of the invention could be used to select a catalytic RNA having a specific ribonuclease activity from a pool of RNA molecules [Bartel, 1993].

The isolated nucleic acids and antisense nucleic acids of the invention can be used to construct recombinant expression vectors as described previously. These recombinant expression vectors are then useful for making transformant host cells containing the recombinant expression vectors, for expressing protein encoded by the nucleic acids of the invention, and for isolating proteins of the invention as described previously. The isolated nucleic acids and antisense nucleic acids of the invention can also be used to construct transgenic and knockout animals as described previously.

The isolated proteins of the invention are useful for making antibodies reactive against proteins having P450RAI-2 activity, as described previously. Alternatively, the antibodies of the invention can be used to isolate a protein of the invention by standard immunoaffinity techniques. Furthermore, the antibodies of the invention, including bispecific antibodies are useful for diagnostic purposes.

Molecules which bind to a protein comprising an amino acid sequence shown in SEQ ID NO:5 can also be used in a method for killing a cell which expresses the protein, wherein the cell takes up the molecule. Preferably, the cell is a tumor cell. Destruction of such cells can be accomplished by labeling the molecule with a substance having toxic or therapeutic activity. The term “substance having toxic or therapeutic activity” as used herein is intended to include molecules whose action can destroy a cell, such as a radioactive isotope, a toxin (e.g. diphtheria toxin or ricin), or a chemotherapeutic drug, as well as cells whose action can destroy a cell, such as a cytotoxic cell. The molecule binding to the P450RAI-2 can be directly coupled to a substance having a toxic or therapeutic activity or may be indirectly linked to the substance. In one example, the toxicity of the molecule taken up by the cell is activated by P450RAI-2 protein.

The invention also provides a diagnostic kit for identifying tumor cells comprising a molecule which binds to a protein comprising an amino acid sequence shown in SEQ ID NO:5, for example, for incubation with a sample of tumor cells; means for detecting the molecule bound to the protein, unreacted protein or unbound molecule; means for determining the amount of protein in the sample; and means for comparing the amount of protein in the sample with a standard. Preferably, the molecule is a monoclonal antibody. In some embodiments of the invention, the detectability of the molecule which binds to P450RAI-2 is activated by said binding (e.g., change in fluorescence spectrum, loss of radioisotopic label). The diagnostic kit can also contain an instruction manual for use of the kit.

The invention further provides a diagnostic kit for identifying tumor cells comprising a nucleotide probe complementary to the sequence, or an oligonucleotide fragment thereof, shown in SEQ ID NO:4, for example, for hybridization with mRNA from a sample of tumor cells; means for detecting the nucleotide probe bound to mRNA in the sample with a standard. The diagnostic kit can also contain an instruction manual for use of the kit.

Discussion of Results

The present inventors have have identified a novel retinoic acid metabolizing cytochrome P450. Consequently, at least two genes, encoding all-trans-RA metabolizing enzymes P450RAI-1 [White, J. A., et al. (1997), White, J., et al. (1998)] and P450RAI-2 are expressed in humans. The predicted amino acid sequences of these enzymes (P450RAI-1 and P450RAI-2) are 42% similar overall. Regions corresponding to functional domains such as those for heme binding and putative substrate binding exhibit the highest degrees of similarity. P450RAI-1 and -2 are also conserved across species from zebrafish to humans suggesting that these enzymes may be functionally distinct [White, J. A., et al. (1997), Nelson, D. (1999); White, J. A. et al. (1996)]. The genomic structures of these two genes are quite distinct-, P450RAI-1 is comprised of 7 exons while P450RAI-2 has 6 and there is no clear evidence of conserved intron/exon boundaries between the two genes [White, J., et al. (1998); Nelson, D. (1999)], These data support the possibility that these genes diverged from a common ancestral gene prior to the emergence of mammals.

P450RAI-2 can metabolize all-trans-RA with efficiency comparable to that of P450RAI-1. HPLC analysis comparing these enzymes reveals their striking similarities with respect to conversion of all-trans-RA into 4-OH- and 4-oxo RA and characteristic secondary products. Moreover, P450RAI-1 and P450RAI-2 share surprisingly similar specificities for retinoids as determined by our competition studies. The all-trans metabolite of RA is clearly the preferred substrate for both enzymes with a rank-order of: all-trans-RA>9 cis RA>13 cis. Other retinoids such as retinol and retinaldehyde are very poor competitors suggesting that they are unlikely to be natural substrates for these enzymes under normal physiological conditions. This is in contrast to a recent report suggesting that P450RAI (CYP26A) may be involved in the activation step of retinol [Lane, M., et al. (1999)]. These similarities would suggest that, at least with respect to metabolic activity, these enzymes may be equivalent. Although this is somewhat surprising given their differences in sequence, there are many RA binding proteins—RARs, RXRs, CRABPs—which are widely different in primary amino acid sequences. It is possible that the differences in sequence reflect differences in the abilities of these enzymes to interact with other proteins such as CRABPs which have been proposed to modify all-transRA metabolic activities in cells [Boylan, J. & Gudas, L. (1992); Napoli, J. (1996)].

Although the enzymatic activities of P450RAI-1 and -2 may be similar, it appears that their tissue specific expression is not. Tissue dot blot and northern blot analyses indicate that in the adult, P450RAI-2 is broadly expressed at low levels in most tissues but is predominantly expressed in brain tissues, notably pons and cerebellum. P450RAI-1, on the other hand, does not show appreciable expression in any of the human brain tissues evaluated. During development numerous studies have indicated that the role of P450RAI-1 is to regulate local levels of all-trans-RA and restrict certain tissues from all-trans-RA activity. Developing retina exhibit an exquisite pattern of coordinated expression of P450RAI-1, and the all-trans-RA synthesizing enzymes RALDH-2 and ALDH-1 [McCafferty et al., (1999)]. Given that the EST corresponding to P450RAI-2 (accession # AA012833) was derived from an adult retinal library suggests that this enzyme may also play a role in the balance of all-trans-RA in retinal tissue.

Expression of P450RAI-2 in adult human brain suggests that all-trans-RA may play an important homeostatic role in brain tissue. In this regard, it has recently been shown that all-trans-RA signaling pathways may be important for memory and learning since RARP/RXR(X knockout mice have impaired long-term potentiation and limited ability to negotiate a water-maze [Chiang, M.Y., (1998)]. If all trans-RA signaling pathways are involved in maintenance of higher order brain function then the regulation and function of enzymes like P450RAI-2 will be important regulators of these pathways. The high level of expression of P450RAI-2 in adult cerebellum suggests that it is protecting this tissue from exposure to RA. Of note, developing cerebellum is highly sensitive to the teratogenic effects of RA [Lammer, E. J., (1985); Lammer, E. & Armstrong, D. (1992)]. Also, Yamamoto et al. [Yamamoto, M., et al. (1998)], have reported evidence that RA may be synthesized from retinol in the choroid plexus of developing cerebellum, and that RA injected into the cerebellum is rapidly metabolized. These findings support the notion of an important role for RA metabolism in cerebellum during development which may also extend into adulthood. It is likely that this metabolism is mediated by P450RAI-2.

Studies of several cell lines in culture indicate that P450RAI-2 expression, similar to that of P450RAI-1, is regulated by all-trans-RA. For example, the induction by all-trans-RA of P450RAI-2 expression in the breast epithelial adenocarcinoma cell line MCF-7 is comparable to that of P450RAI-1. Interestingly, the transcriptional elements required for RA-induction of P450RAI-2 may be different from those for induction of P450RAI-1-, inspection of genomic sequence immediately upstream of the first exon of P450RAI-2 has not revealed any elements previously demonstrated to mediate a retinoid induction of transcription, whereas we have identified a functional, conserved, canonical RA response element (RARE) within the first 200 bp of the P450RAI-1 promoter (M.P.; unpublished). Comparative studies of induction of these two genes at the transcriptional level will help to discriminate possible similarities in their regulation.

RA metabolism may be implicated in certain disease states such as dermatological conditions angiogenesis, immunological disorders, and cancer. The present work suggests that certain brain functions may also depend on normal retinoid metabolism. There is interest in inhibiting this activity to increase the cell sensitivity to the differentiating or apoptotic affects of all-trans-RA; recent clinical trials with all-trans-RA metabolism inhibitors suggest that this may be a viable approach to treat diseases which respond positively to retinoids. The identification of a second P450RAI provides another potentially useful target for rational drug design.

While the present invention has been described with reference to what are presently considered to be the preferred examples, it is to be understood that the invention is not limited to the disclosed examples. To the contrary, the invention is intended to cover various modifications and equivalent arrangements included within the spirit and scope of the appended claims.

All publications, patents and patent applications are herein incorporated by reference in their entirety to the same extent as if each individual publication, patent or patent application was specifically and individually indicated to be incorporated by reference in its entirey.

REFERENCES

Particulars of references cited above are given below. All of the listed references are incorporated herein by referl lence.

-   Abu-Abed, S. S., Beckett, B. R., Chiba, H., Chithalen, J. V., Jones,     G., Metzger, D., Chambon, P., and Petkovich, M. (1998). Mouse     P450RAI (CYP26) expression and retinoic acid-inducible retinoic acid     metabolism in F9 cells are regulated by retinoic acid receptor gamma     and retinoid X receptor alpha. Journal of Biological Chemistry 273,     2409-15. -   Achkar, C. C., Derguini, F., Blumberg, B., Langston, A., Arthur, A.     L., Speck, J., Evans, R. M., Bolado, Jr., J. Nakanishi, K. and     Buck, J. (1996) 4-Oxoreinol, a new natural ligand and transactivator     of the retinoic acid receptors. Proc. Natl. Acad. Sci. USA 93,     4879-84. -   Adamson, P. C., Boylan, J. F., Balis, F. M., Murphy, R. F.,     Godwin, K. A., Gudas, L. J. and Poplack, D. G. (1993). Time course     of induction of metabolism of all-trans retinoic acid and the     up-regulation of cellular retinoic acid-binding protein. Cancer     Research 53, 472-476. -   Akimenko, M. A. and Ekker, M. (1995a). Anterior duplication of the     Sonic hedgehog expression pattern in the pectoral fin buds of     zebrafish treated with retinoic acid. Developmental Biology 170,     243-7. -   Akimenko, M. A., Johnson, S. L., Westerfield, M. and Ekker, M.     (1995b). Differential induction of four msx homeobox genes during     fin development and regeneration in zebrafish. Development 121,     347-57. -   Bartel, D. and Szostak, J. W. (1993). Science 261, 1411-1418. -   Blaner, W. (1994). Retinol and retinoic acid metabolism. In: The     Retinoids. (M. Sporn, Roberts, A. and Goodman, D.S., Editors) Raven     Press, Inc.: New York. -   Bligh, E. G. and Dyer, W. J. (1957). A rapid method of total lipid     extraction and purification. Canadian Journal of Biochemistry 37,     911-917. -   Blumberg, B., Bolado, Jr., J., Derguini, F., Craig, A. G.,     Moreno, T. A., Chakravarti, D., Heyman, R. A., Buck, J. and     Evans, R. M. (1996) Novel retinoic acid receptor ligands in Xenopus     embryos. Proc. Natl. Acad. Sci. USA 93, 4873-78. -   Boss et al., U.S. Pat. No. 4,816,397. -   Boylan, J. & Gudas, L. (1992) J. Biol. Chem. 267, 21486-21491 -   Boylan, J. F., Lufkin, T., Achkar, C. C., Taneha, R., Chambon, P.     and Gudas, L. J. (1995). Targeted Disruption of Retinoic Acid     Receptor a (RARa) and RARg Results in Receptor-Specific Alterations     in Retinoic Acid-Mediated Differentiation and Retinoic Acid     Metabolism. Mol. Cell Biol. 15, 843-851. -   Butler, W. B., and Fontana, J. A. (1992). Responses to retinoic acid     of tamoxifen-sensitive and -resistant sublines of human breast     cancer cell line MCF-7. Cancer Research 52, 6164-7. -   Cabilly et al. U.S. Pat. No. 4,816,567. -   Cech et al., (a) U.S. Pat. No. 4,987,071. -   Cech et al., (b) U.S. Pat. No. 5,116,742. -   Chambon, P. (1995). The molecular and genetic dissection of the     retinoid signaling pathway. [Review]. Recent Progress in Hormone     Research 50, 317-32. -   Chambon, P. (1996) Faseb J. 10, 940-954 -   Chiang, M. Y., Misner, D., Kempermann, G., Schikorski, T., Giguere,     V., Sucov, H. M., Gage, F. H., Stevens, C. F. & Evans, R. M. (1998)     Neuron 21, 1353-1361. -   Chomienne, C., Fenaux and Degos, L. (1996). Retinoid differentiation     therapy in promyelocytic leukemia. FASEB J. 1025-1030. -   Chytil, F. (1984). Retinoic acid: Biochemistry, toxicology,     pharmacology, and therapeutic use. Pharmacol. Rev. 36, 93-99. -   Cole et al. (1985). Monoclonal Antibodies in Cancer Therapy.     Allen R. Bliss, Inc. -   Creech Kraft, J., Schuh, T., Juchau, M. R. and Kimelman, D. (1994).     Temporal distribution, localization and metabolism of all-trans     retinol, didehydroretinol and all-trans retinal during Xenopus     development. Biochem. J. 301, 111-119. -   De Coster, R., Wouters, W. and Bruynseels, J. (1996). P450-dependent     enzymes as targets for prostate cancer therapy. J. Ster. Biochem.     Mol. Biol. 56, 133-43. -   Duell, E. A., Astrom, A., Griffiths, C. E., Chambon, P. and     Voorhees, J. J. (1992). Human skin levels of retinoic acid and     cytochrome p-450-derived 4-hydroxyretinoic acid after topical     application of retinoic acid in vivo compared to concentrations     required to stimulate retinoic acid receptor-mediated transcription     in vitro. Journal of Clinical Investigation 90, 1269-74. -   Fiorella, P. D., Giguere, V. and Napoli, J. L. (1993). Expression of     Cellular Retinoic Acid-binding Protein (Type II) in Escherichia     coli. The Journal of Biological Chemistry 268, 21545-21552. -   Formelli, F., Barua, A. and Olson, J. (1996). Bioactivities of     N-(4-hydroxyphenyl) retinimide and retinoyl B-glucuronide. FASEB J.     10, 1014-1024. -   Frolik, C. A., Roberts, A. B., Tavela, T. E., Roller, P. P.,     Newton, D. L. and Sporn, M. B. (1979). Isolation and identification     of 4-hydroxy- and 4-oxoretinoic acid. In vitro metabolites of     all-trans retinoic acid in hamster trachea and liver. Biochemistry     18, 2092-7. -   Fujii, H., Sato, T., Kaneko, S., Gotoh, O., Fujii-Kuriyama, Y.,     Osawa, K., Kato, S., and Hamada, H. (1997). Metabolic inactivation     of retinoic acid by a novel P450 differentially expressed in     developing mouse embryos. EMBO Journal 16, 4163-73. -   Gudas, L., Sporn, M. and Roberts, A. (1994). Cellular biology and     biochemistry of the retinoids. In: The Retinoids. (M. Sporn,     Roberts, A. and Goodman, D. S., Editors) Raven Press, Inc.: New     York. -   Guengerich, (1991) J. Biol. Chem. 266:10019-10022 -   Higgins, D. G. and Sharp, P. M. (1989). Fast and sensitive multiple     sequence alignments on a microcomputer. CABIOS 5, 151-153. -   Higgins, D. G., Bleasby, A. J., and Fuchs, R. (1991). CLUSTAL V:     improved software for multiple sequence alignment. CABIOS 8,     189-191. -   Hogan, B. et al., (1986). A Laboratory Manual, Cold Spring Harbor,     N.Y., Cold Spring Harbor Laboratory. -   Hollermann, T., Chen, Y., Grunz, H., and Pieler, T. (1998).     Regionalized metabolic activity establishes boundaries of retinoic     acid signalling. European Molecular Biology Organization 17,     7361-7372. -   Hong, W. (1994). Retinoids and human cancer. In: The Retinoids. (M.     Sporn, Roberts, A. and Goodman, D. S., Editors) Raven Press, Inc.:     New York. -   Houbenwcyl, (1987). Methods of Organic Chemistry, ed. E. Wansch.     Vol. 15 I and II. Thieme, Stuttgart. -   Hozumi, N and Sandhu, J. S. (1993). Recombinant antibody technology,     its advent and advances. Cancer Invest. 11, 714-723. -   Huse et al., (1989). Science 246, 1275-1281. -   Iulianella, A., Beckett, B., Petkovich, M., and Lohnes, D. (1999). A     molecular basis for retinoic acid-induced axial truncation.     Developmental Biology 205, 33-48. -   Jones, G., Ramshaw, H., Zhang, A., Cook, R., Byford, V., White, J. &     Petkovich, M (1999) Endocrinology 140, 3303-3310. -   Kennett, R. (1979). Cell fusion. Methods Enzymol. 58, 345-359. -   Kohler and Milstein. (1975). Nature 256, 495-497. -   Kozbor et al. (1983). Immunol. Today 4, 72. -   Lammer, E. j., Chen, D. T., Hoar, R. M., Agnish, N. D., Benke, P.     J., Braun, J. T., curry, C. J., Fernhoff, P. M., Grix, A. J.,     Lott, I. T. & et, a. 1. (1985) N. Engl. J. Med. 313, 837-841. -   Lammer, E. & Armstrong, D. (1992) in Retinoids in normal development     and teratogenesis, ed. Morris-Kay, G. (Oxford University Press,     Oxford), pp. 281-295. -   Lane, M., Chen, A., Roman, S., Derguini, F. & Gudas, L. (1999) Proc.     Natl. Acad. Sci. USA 96, 13524-13529. -   Lemoine, N. R. and Cooper, D. N. (1996). Gene Therapy, Human     Molecular Genetics Series, BIOS Scientific Publishers, Oxford, U.K. -   Leo et al. (1989). Metabolism of retinol and retinoic acid by human     liver cytochrome P450IIC8. Arch. Biochem. Biophys. 269, 305-312. -   Lippman, S. M., Heyman, R. A., Kurie, J. M., Benner, S. E. and     Hong, W. K. (1995). Retinoids and chemoprevention: clinical and     basic studies. J. Cellular Biochem. Supplement 22, 1-10. -   Lotan, R. M. (1995). Squamous differentiation and retinoids. Cancer     Treat. Res. 74, 43-72. -   Lotan, R. (1996). Retinoids in Cancer Chemoprevention. Faseb J. 10,     1031-1039. -   Maden, M. and Holder, N. (1992). Retinoic acid and development of     the central nervous system. [Review]. Bioessays 14, 431-8. -   Mangelsdorf, D. J. and Evans, R. M. (1995). The RXR Heterodimers and     Orphan Receptors. Cell 83, 841-850. -   Merrifield, (1964]. J. Am. Chem. Assoc. 85, 2149-2154. -   McCafferty et al., (1990). Nature 348, 552-554. -   Mirski, S. and Cole, S. P. C. (1989). Antigens associated with     multidrug resistance in H69AR, a small cell lung cancer cell line.     Cancer Res. 49, 5719-5724. -   Monia, B. P., Johnston, J. F., Geiger, T., Muller, M. and Fabbro, D.     (1996). Antitumor activity of a phosphorothioate antisense     oligodeoxynucleotide targeted against C-raf kinase. Nature Medicine     2, 668-75. -   Moon, R. C., Mehta, R. G. and Rao, K. V. N. (1994). Retinoids and     cancer in experimental animals. In: The Retinoids. (M. Sporn,     Roberts, A. and Goodman, D.S., Editors) Raven Press, Inc.: New York. -   Morriss-Kay, G. M. (1996). Embryonic development and pattern     formation. FASEB J. 10, 961-968. -   Morrison et al., (1985). Proc. Natl. Acad. Sci. USA 81, 6851. -   Muindi, J. R. F., Frankel, S. R., Huselton, C., DeGrazia, F.,     Garland, W., Young, C. W. and Warrell, R. P., Jr. (1992). Clinical     pharmacology of oral all-trans retinoic acid in patients with acute     promyelocytic leukemia. Cancer Research 52, 2138-2142. -   Muindi, J. R., Young, C. W. and Warrell, R. J. (1994a). Clinical     pharmacology of all-trans retinoic acid. Leukemia 8, 1807-1812. -   Muindi, J. R., Young, C. W. and Warrell, R. J. (1994b). Clinical     pharmacology of all-trans retinoic acid. Leukemia 8, s16-s21. -   Napoli, J. L., Boerman, M. H., Chai, X., Zhai, Y. and     Fiorella, P. D. (1995). Enzymes and binding proteins affecting     retinoic acid concentrations. J. Ster. Biochem. Mol. Biol. 53,     497-502. -   Napoli, J. (1996). Retinoic acid biosynthesis and metabolism.     FASEB J. 10, 993-1001. -   Nebert et al. (1989), DNA 8:1-13 -   Nelson, D. et al (1996), Pharmacogenetics 6:1-42 -   Nelson, D. (1999a) Arch. Biochem. Biophys 369: 1-10 -   Nelson, D. (1999b) Arch. Biochem. Biophys. 371, 345-347. -   Niederreither, K., Subbarayan, V., Dolle, P. & Chambon, P. (1999)     Nature Genetics 21, 444-448. -   Old, R. W. and Primrose, S. B., In: Principles of Gene Manipulation.     An Introduction to Genetic Engineering, 4th ed. Oxford University     Press. 63-66. -   Ohno, C. K. and Petkovich, M. (1993). FTZ-F1 beta, a novel member of     the Drosophila nuclear receptor family. Mechanisms of Development     40, 13-24. -   Pijnappel, W. W., Hendriks, H. F., Folkers, G. E., van den Brink,     C., Dekker, E. J., Edelenbosch, C., van der Saag, P. and     Durston, A. J. (1993). The retinoid ligand 4-oxo-retinoic acid is a     highly active modulator of positional specification. Nature 366,     340-4. -   Ray, W. J., Bain, G., Yao, M., and Gottlieb, D. I. (1997). CYP26, a     novel mammalian cytochrome P450, is induced by retinoic acid and     defines a new family. Journal of Biological Chemistry 272, 18702-8. -   Reddy, A. P., Chen, J., Zacharewski, T., Gronemeyer, H.,     Voorhees, J. J. and Fisher, G. J. (1992). Characterization and     purification of human retinoic acid receptor-g1 overexpressed in the     baculovirus-insect cell system. Biochem. J. 287, 833-840. -   Rigas, J., Miller, V., Zhang, Z. F., Klimstra, D., Tong, W.,     Kris, M. and Warrell, R. (1996). Metabolic phenotypes of retinoic     acid and the risk of lung cancer. Cancer Res. 56, 2692-2696. -   Roberts, A. B., Nichols, M. D., Newton, D. L. and Sporn, M. B.     (1979a). In vitro metabolism of retinoic acid in hamster intestine     and liver. Journal of Biological Chemistry 254, 6296-302. -   Roberts, A. B., Frolik, C. A., Nichols, M. D. and Sporn, M. B.     (1979b). Retinoid-dependent induction of the in vivo and in vitro     metabolism of retinoic acid in tissues of the vitamin A-deficient     hamster. Journal of Biological Chemistry 254, 6303-9. -   Sambrook, J., Fritsch E. F. and Maniatis, T. (1989). Molecular     Cloning: A Laboratory Manual. Cold Spring Harbor Lab Press, Cold     Spring Harbor, N.Y. -   Staerz & Bevan (1986a). Proc. Natl. Acad. Sci. (USA) 83, 1453. -   Staerz & Bevan (1986b). Immunology Today 7, 241. -   Stewart, A. J., Canitrot, Y., Baracchini, E., Dean, N. M.,     Deeley, R. G., and Cole, S. P. C. (1996). Reduction of Expression of     the multidrug resistance protein (MRP) in human tumor cells by     antisense phophorothioate oligonucleotides. Biochem. Pharamcol. 51,     461-469. -   Swindell, E., Thaller, C., Sockanathan, S., Petkovich, M.,     Jessell, T. & Eichele, G. (1999) Dev. Biol. 216, 282-296. -   Takatsuka, J., Takahashi, N. and De Luca, L. M. (1996). Retinoic     Acid Metabolism and Inhibition of Cell Proliferation: An Unexpected     Liaison. Cancer Research 56, 675-678. -   Takeda et al., (1985). Nature 314, 452. -   Tanaguchi et al., European Patent Publication EP171496. -   Teng, et al. (1982) Meth. Enzymol. 92. 3-16. -   Thompson, J. D., Higgins, D. G., and Gibson, T. J. (1994). CLUSTAL     W: improving the sensitivity of progressive multiple sequence     alignment through sequence weighting, positions-specific gap     penalties and weight matrix choice. Nucleic Acids Research 22,     4673-4680. -   Van Wauwe, J. P., Coene, M.-C., Goossens, J., Van Nijen, G.,     Cools, W. and Lauwers, W. (1988). Ketoconazole inhibits the in vitro     and in vivo metabolism of all-trans retinoic acid. The Journal of     Pharmacology and Experimental Therapeutics 245, 718-722. -   Van Wauwe, J. P., Coene, M.-C., Goossens, J., Cools, W. and     Monbaliu, J. (1990). Effects of cytochrome P450 inhibitors on the in     vivo metabolism of all-trans-retinoic acid in rats. The Journal of     Pharmacology and Experimental Therapeutics 252, 365-369. -   Van Wauwe, J., Van Nyen, G., Coene, M., Stoppie, P., Cools, W.,     Goossens, J., Borghgraef, P. and Janssen, P. A. J. (1992).     Liarazole, an Inhibitor of Retinoic Acid Metabolism, Exerts     Retinoid-Mimetic Effects in Vivo. The Journal of Pharmacology and     Experimental Therapeutics 261, 773-779. -   Ward et al., (1989). Nature 341. 544-546. -   Warrell, R. J. (1994). Applications for retinoids in cancer therapy.     Seminars in Hematol. 31, 1-13. -   Warrell, R. J., Maslak, P., Eardley, A., Heller, G., Miller, W. J.     and Frankel, S. R. (1994). Treatment of acute promyelocytic leukemia     with all-trans retinoic acid: an update of the New York experience.     Leukemia 8, 929-933. -   White, J. A., Boffa, M. B., Jones, B. and Petkovich, M. (1994). A     zebrafish retinoic acid receptor expressed in the regenerating     caudal fin. Development 120, 1861-72. -   White, J. A., Guo, Y., Baetz, K., Beckett-Jones, B., Bonasoro, J.,     Hsu, K., Dilworth, J., Jones, G., and Petkovich, M. (1996a).     Identification of the retinoic acid-inducible all trans retinoic     acid 4-hydroxylase. Journal of Biological Chemistry 271,     29922-29927. -   White, J. & Petkovich, M. (1996b) Met. Mol. Biol. 89, 389-404. -   White, J. A., Beckett-Jones, B., Guo, Y. D., Dilworth, F. J.,     Bonasoro, J., Jones, G., and Petkovich, M. (1997). cDNA cloning of     human retinoic acid-metabolizing enzyme (hP450RAI) identifies a     novel family of cytochromes P450. Journal of Biological Chemistry     272, 18538-41. -   White, J., Beckett, B., Scherer, S., Hebrick, J. and     Petkovick, M. (1998) Genomics 48, 270-272. -   Williams, J. B. and Napoli, J. L. (1987). Inhibition of retinoic     acid metabolism by imidazole antimycotics in F9 embryonal carcinoma     cells. Biochemical Pharmacology 36, 1386-1388. -   Wouters, W., van, D. J., Dillen, A., Coene, M. C., Cools, W. and     De, C. R. (1992). Effects of liarazole, a new antitumoral compound,     on retinoic acid-induced inhibition of cell growth and on retinoic     acid metabolism in MCF-7 human breast cancer cells. Cancer Research     52, 2841-6.NCES -   Yamamoto, M., Drager, U., Ong, D. & McCaffery, P. (1998) Eur. J.     Biochem. 257, 344-350. 

1-137. (canceled)
 138. An isolated nucleic acid molecule of claim 243 that encodes a protein that oxidizes a retinoid.
 139. An isolated nucleic acid molecule that is at least about 90 percent homologous to the nucleic acid molecule as shown in SEQ ID No:4.
 140. An isolated nucleic acid molecule of claim 243 wherein the nucleic acid molecule encodes a protein that oxidizes a retinoid at the 4-position of the β-ionone ring.
 141. An isolated nucleic acid molecule of claim 140, wherein the nucleic acid encodes a protein that of hydroxylates a retinoid at the 4-position of the β-ionone ring.
 142. An isolated nucleic acid molecule of claim 141 wherein said retinoid is a retinoic acid.
 143. A vector comprising a nucleic acid molecule of claim
 243. 144. A vector comprising a nucleic acid molecule of claim
 139. 145. The vector of claim 143, wherein the vector is a pT-Adv vector or a pcDNA3.1 vector.
 146. The vector of claim 145 that is pcDNA3.1-P450RAI-2.
 147. A host cell transformed with a vector of claim
 143. 148. A host cell transformed with the vector of claim
 134. 149. The host cell of claim 147 wherein the cell is a TOP10F′ E. coli and the vector is pcDNA3.1
 150. An isolated all-trans retinoic acid metabolizing cytochrome P450 peptide having the amino acid sequence of SEQ. ID. NO. 5: at least about 90% homologous to the amino acid sequence of SEQ. ID. NO. 5, that is a functionally equivalent fragment of the peptide having the amino acid sequence of SEQ. ID. NO. 5 or that is is an analog, homolog or derivative of the peptide having the amino acid sequence of SEQ. ID. NO.
 5. 151. A stably transfected cell line which expresses a protein encoded by a nucleic acid molecule of claim
 243. 152. A culture of cells transformed with a recombinant DNA molecule comprising a nucleotide sequence according to claim
 243. 153. A culture of cells according to claim 152, wherein the cells are eukaryotic.
 154. A process for producing an all-trans retinoic acid metabolizing cytochrome P450 polypeptide, P450RAI-2 protein, the process comprising the steps of: (i) preparing a DNA fragment including a nucleic acid molecule according to claim 243 which encodes said protein; (ii) incorporating the DNA fragment into an expression vector to obtain a recombinant DNA molecule which includes the DNA fragment and is capable of undergoing replication; (iii) transforming a host cell with said recombinant DNA molecule to produce a transformant which can express said protein; (iv) culturing the transformant to produce said protein; and (v) recovering said protein from resulting cultured mixture.
 155. An antibody to a protein of claim
 150. 156. An antibody of claim 155 wherein the antibody is a monoclonal antibody.
 157. A method for metabolizing retinoic acid in an organism or cell comprising administering a protein of claim 150 to said organism or cell.
 158. A method for inhibiting retinoic acid hydroxylation in an organism in need of such inhibition, comprising administering to the organism an effective amount of an antisense nucleic acid or oligonucleotide substantially complementary to at least a portion of the sequence identified as SEQ ID NO:4.
 159. The method of claim 158 wherein the organism is human.
 160. The method of claim 159 wherein the organism is being treated for a disease selected from the group consisting of cancer, actinic keratosis, oral leukoplakia, a secondary tumor of the head and/or neck, a non-small cell lung carcinoma, a basal cell carcinoma, acute promyelocytic leukemia, skin cancer, and a premalignancy associated actinic keratosis, acne, psoriasis and/or ichthyosis.
 161. A kit for determining the presence of a protein according to claim 150 or containing an amino acid sequence as identified by SEQ ID NO: 11 or SEQ ID NO:12, comprising an antibody to said protein linked to a reporter system, wherein the reporter system produces a detectable response when a predetermined amount of the protein and the antibody are bound together.
 162. The kit of claim 161 wherein said protein comprises the amino acid sequence identified as SEQ ID NO:5.
 163. A kit for determining the presence of a first a nucleic acid molecule of claim 243, the kit comprising a second nucleic acid molecule capable of hybridizing with at least a portion of a the first nucleic acid molecule under the high stringency conditions of (a), in which the second nucleic acid molecule is linked to a reporter system wherein the reporter system produces a detectable response when a predetermined amount of the first and second molecules are hybridized together.
 164. A method of screening drugs for their effect on activity of a protein of claim 150 comprising exposing a said protein to a said drug and determining the effect on the activity.
 165. The method of claim 164 wherein the activity is oxidation, hydroxylation of a retinoic acid, or hydroxylation of all-trans retinoic acid.
 166. The method of claim 165 wherein the activity is oxidation of all-trans retinoic acid and the protein comprises SEQ ID NO:5.
 167. A method of screening drugs for their effect on expression of a gene, wherein the gene is an inducible gene containing the nucleotide sequence of claim 134, by all-trans retinoic acid, comprising exposing a eukaryotic cell to a said drug and determining the effect on gene expression.
 168. The method of claim 167, wherein the gene has the nucleotide sequence identified as SEQ ID NO:4.
 169. A drug identified according to the method of claim
 164. 170. A drug identified according to the method of claim
 167. 171. A method for inhibiting retinoic acid metabolism in an organism in need of such inhibition, or in cells obtained from such an organism, comprising administering to the organism an effective amount of a drug of claim
 169. 172. A method for inhibiting retinoic acid metabolism in an organism in need of such inhibition, or in cells obtained from such an organism, comprising administering to the organism an effective amount of a drug of claim
 170. 173. A method of oxidizing a retinoid, the method comprising the step of exposing the retinoid to a protein of claim
 150. 174. The method of claim 173, wherein the protein comprises the amino acid sequence identified as SEQ ID NO:5.
 175. The method of claim 173, wherein the retinoid is a retinoic acid.
 176. The method of claim 175, wherein the retinoic acid is all-trans retinoic acid.
 177. A method of screening a drug for its activity on a protein, the method comprising the steps of: (i) providing a cell line having heterologous DNA encoding a protein of claim 150 incorporated thereinto so as to be capable of expressing said protein; (ii) exposing the cell line to the drug, under conditions in which said protein is expressed in an active form, so as to expose the protein to the drug; and (iii) determining the effect of the drug on the activity of the protein.
 178. The method of claim 177, including the step of exposing the cell line to a substrate of the protein, under conditions in which said protein is expressed in an active form, so as to expose the protein to the substrate.
 179. The method of claim 177, wherein said activity is oxidation.
 180. The method of claim 177, wherein step (ii) includes exposing the cell line to the drug and the substrate simultaneously.
 181. The method of claim 180, wherein the substrate is a retinoid.
 182. The method of claim 181, wherein the retinoid is a retinoic acid.
 183. The method of claim 182, wherein the retinoic acid is all-trans retinoic acid.
 184. The method of any of claims 178, wherein said activity is oxidation of the β-ionone ring of the substrate.
 185. The method of claim 184, wherein said oxidation is hydroxylation.
 186. The method of any of claims 177, wherein said heterologous DNA encodes the protein identified as SEQ ID NO:5.
 187. The method of claim 177, wherein said heterologous DNA comprises the nucleotide sequence identified as SEQ ID NO:4.
 188. A method for screening an agent for its effect on an activity of a first protein relative to its effect on the activity of a second protein, the method comprising the steps of: (a) providing a first protein, wherein said protein is a protein of any one of claim 150; (b) providing a second protein, wherein said second protein is a cytochrome P450; (c) exposing the first protein to the agent; (d) exposing the second protein to the agent; and (e) determining the effect of the agent on the activity of the first protein relative to its effect on the activity of the second protein.
 189. The method of claim 188, wherein said activity of each protein is the ability to oxidize a retinoid.
 190. The method of claim 189, wherein said activity is the ability to oxidize a retinoid at the 4-position of the β-ionone ring.
 191. The method of claim 190, wherein said activity is the ability to hydroxylate a retinoid at the 4-position of the β-ionone ring.
 192. The method of any of claims 191 wherein said retinoid is a retinoic acid.
 193. The method of claim 192, wherein said retinoic acid is all-trans retinoic acid.
 194. The method of any of claims 193 wherein said first protein is a human protein.
 195. The method of claim 194, wherein said first protein comprises the sequence identified as SEQ ID NO:5.
 196. The method of any of claims 188 wherein said second protein is selected from the group of proteins encoded by: (a) a nucleotide sequence that hybridizes under high stringency conditions, wherein high stringency conditions include a wash step of about 0.2×SSC at 50° C., to the nucleotide sequence shown as SEQ ID NO:13 or SEQ ID NO:14, and encodes a protein that oxidizes a retinoid; and (b) a nucleotide sequence that hybridizes under high stringency conditions, wherein high stringency conditions include a wash step of about 0.2×SSC at 50° C., to the nucleotide sequence shown as SEQ ID NO:13 or SEQ ID NO:14, and encodes a protein that hydroxylates retinoic acid at the 4 position of the β-ionone ring.
 197. The method of claim 188, wherein said second protein is a human protein.
 198. The method of claim 198, wherein said second protein comprises the amino acid sequence encoded by the nucleotide sequence identified as SEQ ID NO:13.
 199. The method of any of claims 188 wherein step (c) includes exposing the first protein to a retinoid.
 200. The method of any of claims 188 wherein step (d) includes exposing the second protein to a retinoid.
 201. The method of any of claims to 188 wherein each of steps (c) and (d) includes exposing the first protein to a retinoid.
 202. The method of claim 201, wherein step (c) includes exposing the first protein to said retinoid at various concentrations.
 203. The method of claim 201, wherein step (d) includes exposing the second protein to said retinoid at various concentrations.
 204. The method of claim 201, wherein each of steps (c) and (d) includes exposing the second protein to said retinoid at various concentrations.
 205. The method of claim 201, wherein step (c) includes exposing the first protein to said retinoid at various concentrations of the first protein.
 206. The method of claim 201, wherein step (d) includes exposing the second protein to said retinoid at various concentrations of the second protein.
 207. The method of claim 188, wherein step (c) includes exposing the first protein to said retinoid at various concentrations of the first protein and step (d) includes exposing the second protein to said retinoid at various concentrations of the second protein.
 208. A method for screening an agent for its effect on an activity of a first protein relative to its effect on the activity of a second protein, the method comprising the steps of: (a) providing a group of first cells having expressibly incorporated thereinto heterologous DNA encoding a first protein, said protein being a protein of claim 150; (b) providing a group of second cells having expressibly incorporated thereinto heterologous DNA encoding a second protein, wherein said second protein is a cytochrome P450; (c) exposing the first cells to the agent under conditions in which the first protein is expressed; (d) exposing the second cells to the agent under conditions in which the second protein is expressed; and (e) determining the effect of the agent on the activity of the first protein relative to its effect on the activity of the second protein.
 209. The method of claim 208, wherein step (e) includes monitoring the disappearance of the agent in the presence the first cells and monitoring the disappearance of the agent in the presence of the second cells.
 210. The method of claim 208, wherein step (e) includes monitoring the appearance of an oxidized product or products formed from the agent on exposure to the first cells and monitoring the appearance of the oxidized product or products formed from the agent on exposure to the second cells.
 211. The method of claim 208, wherein step (c) includes exposing the first cells to a substrate of the first protein in the presence of the agent and step (d) includes exposing the second cells to the substrate in the presence of the agent.
 212. The method of claim 211, wherein step (e) includes monitoring the production of a reaction product or products formed from the substrate on exposure to the first protein in step (c) and wherein step (e) includes monitoring the production of the reaction product or products formed from the substrate on exposure to the second protein in step (d).
 213. The method of claim 211, wherein step (e) includes monitoring reduction in the amount of substrate on exposure to the first protein in step (c) and wherein step (e) includes monitoring the reduction in the amount of the substrate on exposure to the second protein in step (d).
 214. The method of claim 211 wherein the substrate is a retinoid, or wherein the substrate is a retinoic acid, or is all-trans retinoic acid.
 215. The method of claim 208, wherein said activity of each protein is the ability to oxidize a retinoid.
 216. The method of claim 215, wherein said activity is the ability to oxidize a retinoid at the 4-position of the β-ionone ring.
 217. The method of claim 216, wherein said activity is the ability to hydroxylate a retinoid at the 4-position of the β-ionone ring.
 218. The method of claim 215, wherein said retinoid is a retinoic acid.
 219. The method of claim 218, wherein said retinoic acid is all-trans retinoic acid.
 220. The method of claim 208 wherein said first protein is a human protein.
 221. The method of claim 220, wherein said first protein comprises the sequence identified as SEQ ID NO:5.
 222. The method of claim 208, wherein said second protein is selected from the group of proteins encoded by: (a) a nucleotide sequence that hybridizes under high stringency conditions, wherein high stringency conditions include a wash step of about 0.2×SSC at 50° C., to the nucleotide sequence shown as SEQ ID NO:13 or SEQ ID NO:14, and encodes a protein that oxidizes a retinoid; and (b) a nucleotide sequence that hybridizes under high stringency conditions, wherein high stringency conditions include a wash step of about 0.2×SSC at 50° C., to the nucleotide sequence shown as SEQ ID NO:13 or SEQ ID NO:14, and encodes a protein that hydroxylates retinoic acid at the 4 position of the β-ionone ring.
 223. The method of claim 222, wherein said second protein is a human protein.
 224. The method of claim 223, wherein said second protein comprises the amino acid sequence encoded by the nucleotide sequence identified as SEQ ID NO:13.
 225. The method of claim 208, wherein step (c) includes exposing the first cells to a retinoid.
 226. The method of claims 208, wherein step (d) includes exposing the second cells to a retinoid.
 227. The method of claim 208, wherein each of steps (c) and (d) includes exposing the first cells to a retinoid.
 228. The method of claim 227, wherein step (c) includes exposing the first cells to said retinoid at various concentrations.
 229. The method of claim 227, wherein step (d) includes exposing the second cells to said retinoid at various concentrations.
 230. The method of claim 227, wherein step (c) includes exposing the first cells to said retinoid at various concentrations and step (d) includes exposing includes exposing the second cells to said retinoid at various concentrations.
 231. A method of inducing in an eukaryotic cell, production of RNA comprising the nucleotide sequence identified as SEQ ID NO:4, the method comprising the steps of: (i) exposing the cell to a retinoid; and (ii) hybridizing the RNA with a probe comprising a nucleic acid molecule comprising a nucleotide sequence of claim
 1. 232. The method of claim 231, wherein the cell is a mammalian cell.
 233. The method of claim 232, wherein the cell is a human cell.
 234. The method of claim 231, wherein the retinoid is a retinoic acid.
 235. The method of claim 234, wherein the retinoic acid is all-trans retinoic acid.
 236. The method of claim 231, wherein said nucleic acid sequence is a non-coding sequence complementary to a coding sequence of a nucleic acid molecule encoding the protein comprising the amino acid sequence identified as SEQ ID NO: 5 and the probe is at least 10 nucleotide residues in length, or the probe is at least 15 nucleotide residues in length, or the probe is at least 20 nucleotide residues in length, or the probe is at least 25 nucleotide residues in length, or the probe is at least 30 nucleotide residues in length, or the probe is at least 35 nucleotide residues in length, or the probe is at least 40 nucleotide residues in length, or the probe is at least 45 nucleotide residues in length, or the probe is at least 50 nucleotide residues in length, or the probe is at least 55 nucleotide residues in length, or the probe is at least 56 nucleotide residues in length, or the prob e is at least 60 nucleotide residues in length.
 237. A method of inducing expression in an eukaryotic cell, a protein comprising the amino acid sequence identified as SEQ ID NO: 5, the method comprising the steps of: (i) exposing a cell that comprises a nucleic acid molecule encoding for said protein and that is capable of expressing said protein to a retinoid in an amount sufficient to induce said expression; and (ii) isolating the protein from the cell.
 238. The method of claim 237, wherein isolating the protein comprises exposing proteins produced by the cell after said exposure step to an antibody which binds specifically to said protein.
 239. The method of claim 237 wherein the cell is a mammalian cell.
 240. The method of claim 237 wherein the cell is a human cell.
 241. The method of claim 237, wherein the retinoid is a retinoic acid.
 242. The method of claim 241, wherein the retinoic acid is all-trans retinoic acid.
 243. An isolated nucleic acid molecule encoding an all-trans retinoic acid metabolizing cytochrome P450 polypeptide P450RAI-2 comprising: (a) a nucleic acid sequence as shown in SEQ ID No:4 wherein T can also be U; (b) a nucleic acid molecule encoding a polypeptide having an amino acid sequence shown in SEQ ID No;5; (c) a nucleic acid sequence that hybridizes under high stringency to the nucleic acid sequence of (a) or (b) wherein said high stringency conditions comprise a wash step of about 0.2×SSC at 50° C.; or (d) a nucleic acid sequence encoding a polypeptide that has at least 60% homology with the amino acid sequence as shown in SEQ ID No:5. 